A clinical evaluation of a new cephalosporin, cephazolin, in obstetric patients is presented. Sixteen cardiac patients received the drug prophylactically as antibiotic cover during labour. Eighteen patients with miscellaneous antenatal and puerperal infections received the drug as primary treatment. The data obtained indicate adequate serum and tissue levels with the dose used, and corresponding clinical response. The impression is of a safe and efficaceous drug in the described obstetric situations requiring antibiotic therapy. It may be given prophylactically and with confidence to the cardiac patient in labour.