The safety of ceftriaxone was compared with that of amoxicillin in a randomized study of 91 patients with community-acquired pneumonia. The origin of infection was similar in the two groups. It was proven or probable Streptococcus pneumoniae in 50 percent of the patients and remained uncertain in 40 percent. Ninety percent of the patients who received ceftriaxone were clinically cured compared with 69 percent of those given amoxicillin (p less than 0.05). However, this difference was not apparent among the patients with proven or probable pneumococcal pneumonia. No severe clinical side effects were observed. Cutaneous reactions were more prevalent in the amoxicillin group, whereas mild diarrhea and mucosal candidiasis were more frequent in the ceftriaxone group. Reversible neutropenia was observed in two patients treated with ceftriaxone and none of those treated with amoxicillin.