Blood banks represent a recruitment source with relatively high volumes of initial contacts and entries, a low ratio of entries to initial contacts and a relatively low effort level requirement for the recruitment team. For the CPPT, blood banks were used to some extent by all centers; they provided 26% of initial contacts and 15% of first protocol visits and entries. Probably the most critical determinant of a successful collaboration was the early negotiation with the blood bank director. Several features seemed to characterize successful LRC/blood bank collaborations: Blood banks that were willing to release names and addresses to the LRC, provided staff support, did not request monetary reimbursement, and agreed, sometimes enthusiastically, to participate in joint media campaigns tended to produce the most referrals. Blood banks are well adapted to identify healthy, asymptomatic men with an abnormal laboratory finding identifiable by a blood test.