Cefaclor is a new potent cephalosporin. After oral administration of single doses to non-patient volunteers the antibiotic was well absorbed and excreted unchanged in the urine. Higher peak plasma levels were obtained in fasted subjects. Cefaclor was well tolerated and there were no significant side-effects. Its pharmacokinetic and anti-microbial profile suggest that it may be useful in the treatment of susceptible infections.