BACKGROUND Conventional peritoneal dialysates are potentially bioincompatible and seem to be a causative factor for peritoneal sclerosis. Recent studies demonstrated that a new type of dialysate has a positive long-term clinical effect on dialysis patients. METHODS In this study, to elucidate the short-term biological effects of a newly developed dialysate of higher pH on the peritoneal membrane, we assessed macrophage proportions and several markers (inflammatory cytokines, cancer antigen 125 (CA125) and albumin) in spent dialysates before and 2 weeks after the change to the new fluid from a conventional fluid. RESULTS We found that the use of the new dialysate decreased intraperitoneal levels of inflammatory cytokines, CA125 and albumin associated with the decrease of macrophage populations in dialysis effluents. CONCLUSIONS These observations suggest that a new and less acidic fluid reduces pro-inflammatory potential in the peritoneum, and thus affords better preservation of peritoneal membrane integrity in uremic patients on peritoneal dialysis.