SM-4300, a newly developed human immunoglobulin preparation was evaluated in 24 patients with severe bacterial infections and the following results were obtained. The clinical efficacy was excellent in 4 cases, good in 7, fair in 5, poor in 3 and unknown in 5 with the effective rate of 57.9%. No serious side effect nor abnormalities in laboratory findings due to administration of SM-4300 were observed except 1 case with slight elevation of GOT and GPT.