This study aimed to investigate the effects of 15-deoxyspergualin (DSG), tacrolimus (FK 506) and cyclosporin A (CyA), alone or in combination, on delayed xenograft rejection (DXR). We used the guinea-pig-to-C6-deficient (C6-)-PVG-rat heart transplantation model, since in this strain combination, hyperacute rejection is avoided. In C6- control rats, the guinea pig xenografts survived for 39.2 +/- 6.3 h (mean +/- SD). Splenectomy alone resulted in a xenograft survival of 71.8 +/- 7.8 h, but the addition of CyA or FK 506 did not further improve graft survival (73.6 +/- 3.0 h and 72.0 +/- 17.6 h, respectively). In contrast, DSG treatment increased graft survival to a mean of 99.8 +/- 9.2 h. When CyA or FK 506 was combined with DSG, no additional effects were observed (105 +/- 24.3 h and 95.1 +/- 5.6 h, respectively). DSG alone or in combination with FK 506 or CyA resulted in a significant reduction in the serum IgM levels and reduced the deposits of IgM and IgG in rejected grafts. However, all xenografts were still heavily infiltrated by ED1 + macrophages, regardless of the treatment used. Thus, DSG treatment resulted in moderate prolongation of xenograft survival in C6- rats. The effect seems to be related to suppression of xenoreactive antibody production. To prolong xenograft survival further, strategies that inhibit macrophage infiltration seem required.