Peritoneal solute equilibration studies during prolonged intraperitoneal dwell were performed in patients with psoriasis and normal renal function, and compared to patients with renal failure undergoing peritoneal dialysis. Calcium, phosphorous, uric acid and protein equilibration were faster in uremics. No differences were observed for sodium and chloride. Mass transfer area coefficients (a measure of the mass transfer at infinite dialysate flow rates) were calculated for glucose, protein and uric acid and found to be complimentary to the results obtained by studies of solute equilibration. Possible reasons for the differences obtained are discussed.