To discover if the management of peritonitis in continuous ambulatory peritoneal dialysis (CAPD) may be effectively simplified by single daily i.p. administration of aztreonam (A) and cefuroxime (C), 10 adult CAPD patients (pts) with peritonitis were trained to start the following treatment procedure: a) sterile collection of dialysate effluent for cultures; b) 4 rapid in-and-out exchanges with antibiotic free dialysate; c) addition of 2 g C and 2 g A to a 2-L exchange for 6-h dwell time (the same dosage was repeated once a day in the overnight exchange); d) routine CAPD exchanges. Concentrations of C and A were measured in dialysate and serum of the patients 2, 12, 18, and 21-23 h after the i.p. administration: C remained within therapeutic range in all samples, while serum and dialysate A levels fell below such range 16 h after the i.p. administration. Seventeen peritonitis episodes occurred during the observation period (12 months): initial dialysate cultures grew Staph. aureus in 6 episodes, Staph epidermidis in 6, Pseudomonas aer. in 2, Streptococcus faecalis in 1, Citrobacter in 1, and Candida in 1. All patients but 1 (with Candida-positive culture) responded to this treatment with no relapse in 2 months. We conclude that once a day i.p. administration of 2 g aztreonam plus 2 g of cefuroxime is an effective and simple way of treating CAPD pts with gram-positive and gram-negative peritonitis.