In a multicentre, double-blind, randomized study involving four general hospitals in Israel, the efficacy and safety of ceftriaxone 1 g/day i.v. was compared to that of 2 g/day i.v. in the treatment of moderate to severe community-acquired infections requiring hospitalization. Two hundred and twenty-two patients were enrolled; 112 received intravenous ceftriaxone 1 g/day, and 110 received 2 g/day. The two groups were matched demographically, and their mean APACHE II score (10 points) and mean duration of successful therapy (7 days) were identical. The sites of infection in the 1 g and 2 g groups respectively were lower respiratory tract in 57 versus 51 patients, urinary tract in 31 versus 40 patients, and soft tissue in 24 versus 19 patients. There were no significant differences in clinical outcome between the 1 g and 2 g groups, the outcome being cure in 91% versus 86% of patients, improvement in 3% versus 3% of patients, failure in 3% versus 8% of patients, and relapse in 3% versus 3% of patients. The findings of this study indicate that ceftriaxone 1 g/day is as effective as 2 g/day in the treatment of moderate to severe community-acquired infections. The low-dose form is a more economical means of treating these infections.