To study the life-threatening pneumonia occurred within 1 month after renal transplantation, we evaluated retrospectively 6 pneumonic patients among 38 cyclosporine treated renal allograft recipients who underwent renal transplants from May, 1984 to December, 1985. The results are summerized as follows: 1) Six episodes of severe pneumonia(16%) occurred within 1 month after renal transplantation in 38 renal allograft recipients, and the all patient was recovered. 2) The life-threatening pneumonia developed during 1 month following transplantation and, the clinical deterioration was rapid, serious and the clinical course was long time from 32 days to 86 days. 3) In this group of patients with posttransplantation pneumonia the opportunistic invaders in most cases were bacterial; serratia marcescens, streptococcus viridans in four cases, and klebsiella pneumoniae in three eases. Also the fungi were frequent offending organism; candida in four cases, aspergillus in 2 cases. 4) Although each patient in this series was gravely ill, usually with extensive pulmonary involvement in the chest x-ray findings, the out- come of pneumonia was fully recovered. 5) Proper management included rapid diagnosis, prompt initiation of appropriate antimicrobial agents and, when possible, reduction in the intensity of immunosuppressive therapy. In cases of necessity to administer antibiotics prior to identify causative agents in posttransplant pneumonia, the combination of 3rd generation cephalosporin and aminoglycoside (amikacin) may be most effective.