16 patients with acute urinary tract infections, 6 with acute lower respiratory tract infections and 3 with miscellaneous infections were treated with 1 g cefazolin parenterally 3 times daily. All patients, except one in whom therapy was discontinued, were cured. Both intramuscular and intravenous administration resulted in high-peak serum levels, and concentrations after 8 h were still inhibitory to relevant pathogens. The drug was well tolerated and caused, after intramuscular injection, probably less pain than does cephalotin. Cefazolin is a rational choice of therapy in severe cases of acute urinary, respiratory, and other infections.