The kinetics of peritoneal dialysis with dialysis fluid containing either glucose (1.36, 2.27, or 3.86 g/dl) or glycerol (0.85, 1.40, or 2.50 g/dl) as an osmotic agent was investigated in 24 single dwell studies of 360 min on four uremic patients. To compare the effects of glycerol and glucose on the transport of fluid and solutes across the peritoneal barrier, a new mathematical method for calculation of intraperitoneal dialysate volumes and diffusive mass transport coefficients (KBD) was developed. Radioisotopically tagged albumin (RISA) was added to the dialysate and the rate of fluid transfer was determined by the dilution principle with corrections applied for elimination of RISA from the peritoneal cavity. The elimination rate of RISA varied between 1 and 2 ml/min. KBD values for urea, creatinine, glucose, glycerol, and total protein were calculated during dialysate isovolemia. Glycerol appeared to increase the peritoneal permeability as indicated by an increased KBD value for total protein. The osmotic effect during the initial part of the dwell was similar to that of glucose, but the duration of effective ultrafiltration was shorter because glycerol was absorbed more rapidly than glucose, and ultrafiltered volumes after 6 h were significantly smaller than with glucose.