SummaryLymphoproliferati ve diseases may occur as a complication of severe immunosuppression. In our own center two out of 46 heart transplant recipients, receiving a cyclosporin A containing immunosuppressive regimen, presented with this complication and are reported here. Hepatic involvement and an occult small bowel localisation, which only became evident after a chemotherapy-induced small bowel perforation, illustrate the predilection of posttrans-plant lymphoproliferations for extranodal sites. Both cases represent the extremes of a spectrum of post-transplant lymphoproliferations ranging from polyclonal benign lesions to monoclonal malignant lymphomas. Their B-cell origin was pathologically established, but in none of the two repotted cases the previously postulated role of Epstein-Barr virus in the pathogenesis could be confirmed by serological tests. Severe immunosuppression played a major role in the pathogenesis of these disorders, as suggested by concomitant opportunistic infections occurring in both cases.The lymphoproliferation diagnosed in the polyclonal stage was reversible after reduction of the immunosuppressive therapy, without subsequent graft