In 1984 the second part of the Transfusion Safety Study, the prospective study, was initiated by NHLBI under a separate request for proposal. The testing of the 201,000 serum specimens in the donor repository for antibody to HIV was carried out by laboratories in the prospective study. Those donors confirmed to be anti-HIV positive and matching donors confirmed to be anti-HIV negative were recruited as TSS subjects. Recipients of blood from the positive donors and the negative donors were also recruited as subjects.