PCT Newsletter

March 2026 | No. 03/2026

Practical Advice 

Options and consequences when the International Searching Authority finds a lack of unity of invention 

Q: The International Searching Authority (ISA) has found that the PCT application I filed does not comply with the requirement of unity of invention. It has sent me partial search results with an invitation to pay additional fees within one month (Form PCT/ISA/206). I do not agree with this finding. What options do I have?
A: A PCT application must relate to one invention only or to a group of inventions so linked as to form a single general inventive concept (PCT Articles 3(4)(iii) and 17(3)(a), PCT Rule 13.1). This is referred to in PCT terminology as “unity of invention.” Whether an application complies with the requirement of unity of invention must be determined in accordance with the interpretation of unity of invention contained in Annex B of the Administrative Instructions under the PCT (Section 206 of the Administrative Instructions). If the ISA considers that the international application does not comply with the requirement, it will initially search the parts of the international application which relate to the invention first mentioned in the claims (“the main invention”). Under PCT Article 17(3)(a), it will also invite the applicant to pay additional fees for each additional invention that has not been searched (Form PCT/ISA/206). 
The invitation to pay additional fees that you have received should specify the reasons why the international application does not comply with the requirement of unity of invention, the amount of additional fees to be paid, and the date by which you must pay the fees, which is one month from the date of the invitation (PCT Rule 40.1). This time limit is strict and cannot normally be extended, noting that the ISA has a time limit for establishing the international search report and written opinion (PCT Rules 42 and 43bis.1(a)). If you would like the ISA to search the additional inventions, the fees must be paid within the time limit. 
If you disagree with the determination of lack of unity of invention and would like to challenge the finding, you need to pay the additional fees for the inventions that you would like the ISA to search under protest (PCT Rule 40.2(c)). The protest is a statement which you submit to argue that your application complies with the requirement of unity of invention or that the amount of the required additional fees is excessive – in other words, you believe that there are fewer inventions or groups of inventions than the corresponding amount of additional fees requested. The ISA may charge a protest fee (PCT Rule 40.2(e)); if so, the ISA will also specify this in the invitation and you must also pay the protest fee within one month of receiving the invitation. The amounts of the applicable search fee and protest fee may be found in the PCT Applicant’s Guide, Annex D for those ISAs that charge them (not all ISAs require payment of a protest fee).
If the applicable protest fee is paid within the time limit, a review body constituted within the ISA will review the protest and, if it concludes that the protest is justified, will order total or partial reimbursement of the fees in question including any protest fee.1  You may also request that the text of the protest and the related decision be notified to the designated Offices, but you will be required to furnish any translation of the text and decision that each designated Office may require (PCT Rule 40.2(c)).
The ISA will establish the international search report on the main invention and any parts of the international application relating to the other inventions for which the additional fees have been paid within the time limit (PCT Article 17(3)(a)). It will not search claims that in its view are not part of the main invention unless the additional fees have been paid in time. Nevertheless, all the claims, including those that have not been searched, will be included in the international application to be published and will be part of the application entering the national phase. Please also note that it is not possible to divide international applications during the international phase.
If you do not pay the additional fees, there is normally no other possibility of having the claims not relating to the main invention searched in the international phase. The International Preliminary Examining Authority (IPEA) is not obliged to examine claims that have not been searched (PCT Rule 66.1(e)) and in practice would not do so. Similarly, requesting a supplementary international search under PCT Rule 45bis will not enable you to have all claims searched, since an Authority specified for supplementary search (SISA) may exclude from supplementary search any claims that were not the subject of the international search (PCT Rule 45bis.5(d)).
The consequences in relation to the unsearched claims will depend on the applicable national law. The law of a designated State may provide that, where the designated Office finds that the ISA’s finding of lack of unity of invention was justified, the Office can consider those parts of the application that have not been searched to have been withdrawn with effect in the country concerned unless a special fee is paid to the Office (PCT Article 17(3)(b)). Under Article 4(G) of the Paris Convention, a designated State must also provide the applicant with the right to divide the patent application into divisional applications and preserve the date of the initial application and the benefit of any right of priority, although national law can specify the conditions where such divisions shall be authorized. For details on specific national requirements, please refer to the National Chapter for each Office in the PCT Applicant’s Guide.
Further information can be found in the Practical Advice in the following issues of the PCT Newsletter:
  • 06/2021: Addressing a finding of lack of unity of invention by the ISA
  • 07/2013: Amending the international application in order to address a finding of lack of unity of invention
  • 09/2008: The consequences of a finding of lack of unity of invention of an international application on (i) the international preliminary examination and (ii) the national phase
  • 08/2008: The consequences of a finding by the ISA of lack of unity of invention
[1] Although an additional fee is required for each separate invention, only one protest fee is payable (where applicable), regardless of the number of additional search fees that you may have been invited to pay.

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