Twenty-six patients with bacterial infections, mainly respiratory infections, were treated with newly developed gamma-globulin preparation (SM-4300), as a combination therapy with some antibiotics. The result was as follows. Clinical effects of 18 cases evaluated were excellent in 1 case (5.6%), good in 10 (55.6%), fair in 4 (22.2%) and poor in 3 (16.7%). No remarkable adverse reactions and abnormal value in laboratory data due to administration of SM-4300 were observed. Significant changes of complement system before and after administration of SM-4300 were not observed. It was considered that SM-4300 was effective as a combination therapy with some antibiotics for the treatment of severe or refractory bacterial infections.