We have studied 85 patients who received a renal transplant for CMV infection as well as for herpes simplex (HSV), herpes zoster (HZ), measles, mumps, rubella and hepatitis B. We found no evidence of primary or secondary infections for the non herpetic viruses except for hepatitis B infection that occurred in 17 per cent of the patients. CMV infection occurred in 87 per cent of the patients while antibody rises to HZ and HSV occurred in 30 and 13 per cent of the patients, respectively. The CMV infections occurred 2 to 4 months after the transplantation (mean time 11.1 weeks) and seemed to trigger the first episode of renal rejection that occurred earlier in the CMV infected group (mean time 12.1 weeks) than in the uninfected group (mean time 18.6 weeks). This difference in time is highly significant, p less than 0.001). However these CMV injections did not decrease the longterm survival of the grafted kidneys.