Clinical efficacy and safety of pareteral sulbactam/ampicillin (SBT/ABPC) was compared with cefotiam (CTM) in a randomized clinical trial of pneumonia in the elderly at 13 National Hospitals of Kyushu island. 37 patients received SBT/ABPC 3 g i.v., b.i.d., and 31 patients received CTM 1 g i.v., b.i.d. for 7 to 14 days. 1. 68 patients (37 for SBT/ABPC and 31 for CTM) were evaluated for safety. No statistical differences were noted in the patients' backgrounds of either group. 2. The clinical efficacy of SBT/ABPC was 96.3% (26/27 cases) while CTM was 75.2% (17/23 cases). This was found to be statistically significant (Fisher's exact test: p < 0.05). 3. 100% of evaluated cases (10 for SBT/ABPC and 4 for CTM) showed bacterial elimination. 4. No side effects were observed in the study. 5. Abnormal laboratory findings were noted in 10.8% (4/37 cases) for SBT/ABPC and 3.2% (1/31 cases) for CTM. The major adverse events were mild elevation of GOT, GPT and A1-P for SBT/ABPC, and mild platelets overproduction for CTM. No statistical differences were noted in both groups. These results are consistent with SBT/ABPC as a highly effective antibiotic in the treatment of elderly patients with pneumonia.