Peritoneal transport rates and net drained volume are reported to be different for peritoneal dialysis (PD) patients with diabetes mellitus (DM) as compared with patients without DM. The difference has been considered to be caused by exposure to high plasma glucose levels before PD initiation. However, the results of previous studies conflict. Transport of small solutes has been reported to be either higher than or similar to that seen in patients without DM, and ultrafiltration to be either similar or lower. No information on free water transport is available. The main problem in earlier reports is the wide variation in duration of PD, which may have influenced the outcomes. In the present study, we compared the results of peritoneal function tests in 10 patients with DM to results in 10 patients without DM. All patients were investigated within the first 4 months of PD treatment. No differences were observed in transcapillary ultrafiltration rate, net ultrafiltration, or lymphatic absorption. Free water transport, estimated using the maximum dip in the dialysate-to-plasma ratio of sodium and quantified by calculating the transport through the ultrasmall pores, showed no differences. Small-solute transport was also similar. These findings imply that a mild chronic hyperglycemic state in the peritoneal vessels does not contribute to important peritoneal changes or to changes in aquaporin-1 function. The influence of continuous treatment with hyperosmolar glucose solutions on the latter is worth investigating.