The authors evaluated the transport kinetics of insulin and inulin administered intraperitoneally to six diabetic patients undergoing continuous ambulatory peritoneal dialysis. The mass transfer coefficients (MTC) calculated from dialysate to blood for 1.5% and 4.25% dextrose dialysate were (ml/min): insulin 2.9 ± 0.9, 2.0 ± 0.5; inulin 3.3 ± 1.4; 2.9 ± 1.7, respectively. The MTC for inulin caluclated from blood to dialysate was 2.0 ± 0.7 ml/min. Because insulin disappears from the peritoneal cavity at a rate similar to inulin, it suggests that insulin transport can be defined by diffusion. The derived MTC values for glucose were not altered by the addition of intraperitoneal insulin. The derived MTCs for eight diabetic to thirteen nondiabetic patients were compaed. The MTC dorived for urea was less among the diabetics (16.6 ± 2.2 vs. 24.6 ± 2.6 p < 0.05), but there were no differences for creatinine, uric acid, glucose, inulin, and protein. The derived values were found to be normally distributed and patients in the upper quartile for one solute were generally in the upper quartile for other solutes.