We describe a case of immune hemolysis due to anti-B occurring in a blood group B patient 16 days after a cadaveric renal transplantation from a blood group O donor. Transfusional support was initially required and the direct antiglobulin test (DAT) remained positive for 80 days. Cyclosporin A (CSA), which was used for rejection prophylaxis in this case, has unique immunosuppressive capabilities which protects transplanted organs from rejection, but which might permit this type of 'graft versus host' reaction.