The clinical and laboratory safety of cefprozil was analyzed with data from 4,227 patients who received the drug in North American and European clinical efficacy trials. Of these patients, 3,016 adults and children received capsules or tablets, while 1,211 patients (mostly children) were treated with cefprozil suspension. Cefprozil was used in single-daily or twice-daily dosing regimens for treatment of infections of the upper and lower respiratory tracts, sinuses, middle ear, urinary tract, and skin and skin structure. The incidence of adverse clinical events and laboratory abnormalities was similar to that associated with use of other oral cephalosporins. Gastrointestinal adverse effects were the predominant adverse clinical event, although the incidence of diarrhea with cefprozil was much lower than that with cephalosporins that are less well absorbed. The data confirm the safety of cefprozil in both adult and pediatric patients.