The tolerogenic effects of immediate pretransplant donor-specific transfusion (DST) with cyclosporine (CsA) have been well described. The purpose of this study was to determine if these effects could be improved upon by the administration of post-transplant DSTs. When added to a 29-day course of CsA, a single DST given 24 hr pretransplant improved graft survival compared to CsA alone (84.9 +/- 12.3 vs 40.0 +/- 8.8 days; P less than 0.05). The administration of an additional DST on post-transplant Days 7, 14, and 21 further improved this survival to 152 +/- 28 days, with 45% of grafts surviving greater than 200 days, until sacrifice. The donor specificity of this effect was demonstrated by the increased survival of second ACI grafts transplanted into Lewis recipients with existing "tolerant" ACI allografts (long-term survivors, or LTS); third-party Buffalo rat hearts transplanted into LTS rats in a similar manner were rejected normally. Loss of graft antigenicity was not seen, as retransplanted ACI hearts obtained from LTS Lewis rats were rejected in a first-order manner. From this we conclude that (1) the addition of multiple post-transplant DSTs improve the enhancement seen with preoperative DST and CsA, (2) loss of graft antigenicity does not contribute to this improved enhancement, and (3) this effect appears to be donor antigen specific.