Cefaclor, a new semisynthetic cephalosporin antibiotic for oral use, was studied by 62 clinical investigators in six 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 tract 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 (1.5%). Of particular clinical interest were the outstanding results obtained in the treatment of otitis media and lower respiratory tract infections.