Rule 28 of the European Patent Office Rules provides that, if an invention concerns a microbiological process or a product thereof that involves use of a micro-organism that is not available to the public and that cannot be described in the European patent application in such manner as to enable the invention to be carried out by a person skilled in the art, then the sufficiency requirement of the European Patent Convention may be met by reference to a culture collection in which that micro-organism has been deposited. The rule requires that the depository institution and the file number of the culture deposit stated in the application must in general be supplied to the EPO within 16 months of the filing date or any claimed priority date. In 1989, a Legal Board of Appeal decision had allowed some deviation of the strict provisions of this rule giving applicants the opportunity to correct a deficiency having regard to information on culture deposits within a further period. This decision was reached by way of reasoning by analogy with certain cases dealing with late filing of other documents.

The question of whether this earlier appealed decision was correct was referred to the Enlarged Board of Appeal in the case Hepatitis A Virus/United States of America II. The Enlarged Board of Appeal concluded that the previous decision was wrong and that there was no grace period available for late submission of information relating to a culture deposit. If the information was not submitted within 16 months of the priority date (or if no priority was claimed within 16 months of the actual EPO filing date), then the specification ran the risk of being insufficient for failure to supply this information. The opponents had argued that failure to provide the American Type Culture Collection (ATCC) deposit number in the specification was a mere formal deficiency and that, since both the applicant's in-house designation and the name of the depository had been given in the application as filed, this was sufficient to identify the organism in question. The Enlarged Board of Appeal, however, concluded that provision of the ATCC accession number of the culture deposit was a substantive rather than a mere formal issue. The reason for this was that Rule 28(2) of the European Patent Office Rules provides that the communication of information about the accession number "shall be considered as constituting the unreserved and irrevocable consent of the applicant to the deposited culture being made available to the public in accordance with this rule". Mere supply of the reference information under which the applicant had designated the culture at the time of submitting it to the ATCC did not carry with it this unreserved and irrevocable consent to make the culture deposit available to the public. (It should be noted that Rule 28bis provides that, up to the grant of the patent, access to the culture deposit by "the public" can be restricted to specific experts on the EPO's list of microbiology experts.)