Imipenem/cilastatin sodium is a new thienamycin class of antibiotic with a broad spectrum of bactericidal activities. It may be a suitable single first-line therapy for the treatment of peritonitis in continuous ambulatory peritoneal dialysis (CAPD) patients. Fifty episodes of CAPD peritonitis were treated with imipenem/cilastatin sodium. On presentation, all patients were given an intravenous loading dose of 1 g of imipenem/cilastatin sodium followed by intraperitoneal imipenem/cilastatin sodium for 10 days. During 1989 (30 episodes), 20 mg imipenem/cilastatin sodium was added to each 2-liter bag of peritoneal dialysis (PD) fluid for 10 days. The primary response rate as defined by polymorphonuclear neutrophils < 100/ml in PD fluid was 90%. Unfortunately, 17% of the peritonitis relapsed within 14 days of stopping antibiotic. The complete cure rate without relapse was therefore 73%. During 1990 (20 episodes), 100 mg imipenem/cilastatin sodium was added to each 2-liter bag of PD fluid for 10 days. The primary response rate was 95%, the complete cure rate without relapse was 85%. Imipenem/cilastatin sodium is an effective single first-line antibiotic for the treatment of peritonitis in CAPD.