Studies of the serological development after 26 renal transplants confirm the high frequency of antibody rises not only against the herpes virus group, but also against other virus groups such as measles, Coxsackie B viruses. These antibody rises correlate with febrile episodes and hepatic dysfunction in which CMV is the most often involved. However, the frequency of antibody rises against various viral antigens without any clinical event to suggest viral etiology; the lack of concomitant virus isolation (except the herpes group), as well as the ocurrence of simultaneous antibody rises against several viruses, all suggest that some of these various antibody rises observed may be related to immunological dysfunction rather than to virus infection.