A retrospective analysis of 533 patients receiving kidney transplantation was performed to study the incidence of infection in the early postoperative period. Mostly localized in the lungs and renal system, bacterial complications arose in 133 patients. As compared with the unproblematic management of the urinary tract infections, 45 pulmonary infections were characterized by difficulties in diagnosis and treatment. Poor graft function was closely related to pulmonary infections: mean creatinine was 2.4 mg% (in patients without pneumonia - 1.5 mg%). Out of 45 patients with pneumonia, the graft failed in 16 patients. 6 patients died as a result of pneumonia. Rapid detection of the pathogenic organism is required, if necessary by invasive diagnosis. The administration of erythromycin before identification of the responsible pathogen may be indicated, in view of the fatal outcome in several patients subsequently diagnosed as having Legionella infection.