Donor seropositivity and prednisolone therapy as risk factors for cytomegalovirus infection and disease in cyclosporin-treated renal allograft recipients. We attempted to assess the importance of blood transfusion, donor seropositivity, and prednisolone therapy as risk factors for cytomegalovirus infection in cyclosporin-treated renal allograft recipients. Primary infection was diagnosed in 27 of 86 patients (31 per cent) and recurrent infection in 27 of 79 patients (34 per cent). Receipt of banked blood from unselected donors after transplantation did not increase the incidence of primary infection in the few transfused patients. Kidney donor seropositivity and maintenance prednisolone in addition to cyclosporin were associated with increases in the incidence of primary or recurrent infection, respectively. Cytomegalovirus infection was clinically mild. Presumed bacterial pneumonias occurred in three patients with recurrent cytomegalovirus infection. The absence of severe cytomegalovirus disease probably reflected the minimal use of prednisolone. Matching of seronegative donors with seronegative recipients seemed unjustifiable in cyclosporin-treated renal transplant patients. 