Cefaclor, a new semisynthetic cephalosporin antibiotic for oral use, was studied by 62 clinical investigators in 6 countries in 1493 adult and paediatric patients. The pooled data reveal that satisfactory clinical responses were obtained in 80% of urinary tract infections, 87% of upper respiratory infections, 90% of cases of otitis media, 99% of lower respiratory tract infections, and 96% of skin and skin structure infections. Administration of this antibiotic was associated with a low incidence of adverse reactions including gastrointestinal (2.6%) and hypersensitivity reactions (1.5%). Of particular clinical interest were the outstanding results obtained in the treatment of otitis media and lower respiratory tract infections.