A method using gel permeation chromatography was evaluated for the quantitation of dextran 70 in dialysate samples containing polyglucose. Dialysate samples containing dextran 70 and polyglucose were pretreated using the enzyme alpha-amylase to selectively hydrolyze the alpha(1-4)-linked polyglucose, while leaving the alpha(1-6)-linked dextran 70 intact. Following sample deproteinization with trichloroacetic acid, dextran 70 was quantitated using gel permeation chromatography with refractive index detection. This method was evaluated for accuracy, precision, specificity, linearity, range, and analyte stability. Adequate method linearity with a correlation of >0.999 was established over the range of dextran 70 concentration from 1 to 0.025 mg/ml. Method precision was approximately 2% R.S.D. and accuracy (% recovery) was approximately 98-100% in the typical sample concentration range (1-0.5 mg/ml). This method was applied to the determination of intraperitoneal fluid kinetics in continuous ambulatory peritoneal dialysis (CAPD) patients administered daily night-time intraperitoneal exchanges with either 7.5% polyglucose or 4.25% dextrose. Dextran 70 was added to the dialysis solutions to yield an initial concentration of 1 mg/ml. Dialysate samples were collected at various times over a 10-h dwell-time and assayed for dextran 70. Intraperitoneal volume profiles based on dextran 70 concentrations and drain volumes were then calculated for each dialysis solution.