Continuous ambulatory peritoneal dialysis (CAPD) might result in peritoneal membrane changes. First, CAPD exposes essentially continuously the peritoneum to peritoneal dialysis solutions. Such solutions differ from the usual extracellular fluid bathing peritoneal tissues. Second, this technique may be complicated by an increased frequency of peritonitis when compared to intermittent peritoneal dialysis. We undertook a prospective study of patients undergoing CAPD to determine if there were decreases in peritoneal clearances and if the peritoneal microcirculation maintained its responsiveness to nitroprusside. Peritoneal transport, as assessed by the clearances of urea, creatinine, inulin, and dialysate protein concentration, with and without nitroprusside addition in the dialysis solution, is unchanged in patients undergoing CAPD for up to 1 year, despite frequent episodes of peritonitis.