Seven hundred fifty patients with acute upper or lower respiratory tract infections were randomly assigned to receive 2 gm of erythromycin ethylsuccinate daily or 1.125 gm of clavulanate-potentiated amoxicillin daily in a single-blind, multicenter study. The efficacy of each formulation was similar, with close to 90% of patients in each treatment group being reported as either cured or improved. Gastrointestinal symptoms were the most commonly reported side effects, their overall incidence being similar in both treatment groups. However, diarrhea occurred more than twice as often in the amoxicillin group than the erythromycin group. In each group, the number of patients failing to complete treatment was similar; the main reasons cited for discontinuation were gastrointestinal symptoms. The results indicate that both erythromycin ethylsuccinate and clavulanate-potentiated amoxicillin are well tolerated and are equally effective for routine empirical treatment of acute respiratory tract infections.