The incidence of infection within six months of cadaveric kidney transplantation was reviewed in 183 consecutive patients. Prior to June, 1985, 91 patients received azathioprine 2 mg/kg/day and prednisone 0.5 mg/kg/day; 63 patients (group A1) also received antilymphocyte globulin 15 mg/kg/day for the first ten days, whereas for the 28 other patients (group A2) antilymphocyte globulin had to be withdrawn before 72 hours because of general intolerance. The next 92 patients received cyclosporine 5-8 mg/kg/day and prednisone 0.25 mg/kg/day (group B). The three groups were similar for all studied parameters except for the number of patients with anti-HLA antibodies. At six months the mortality rate was not significantly different between the three groups. After six months the number of infections per patient was 1.47, 1.03 and 0.84 (p less than 0.01) in groups A1, A2 and B respectively; the percentage of patients developing one or more infections was 81, 58 and 57% (p less than 0.01); bacterial infections: 57, 50 and 34% (p less than 0.01); viral infections: 40, 14 and 10% (p less than 0.01); cytomegalovirus infections: 27, 11 and 4% (p less than 0.001). After adjustment with logistic regression upon factors which might facilitate infections, the results showed a significantly lower incidence of infection for the cyclosporine-treated group, especially for cytomegalovirus, as compared with the antilymphocyte globulin-treated group.