A size exclusion chromatographic method is reported that quantitated PEG 3350 in human plasma and urine to a concentration of 10 μg/ml in plasma, or urine. The chromatographic system consisted of a 500 A gel permeation analytical column, a differential refractometer detector, and chloroform as the eluting solvent. Organic extraction was used as an initial separation technique. PEG 400 was used as the internal standard for PEG 3350, and showed similar extraction properties. Spiked plasma standards yielded standard calibration curves with correlation coefficients of greater than 0.99, and relative standard deviations (n=3) of 2.19% (500 μg/ml) and 6.97% (20 μg/ml). The analytical technique was used to estimate the elimination rate constant of PEG 3350 from 5 normal human subjects after oral administration of 240 grams of PEG 3350. KEwas found to be 0.1079 hr−10.03781−1hr (mean s.d.) using the Sigma-minus data analysis method on total urines collected from the 5 subjects at varying intervals.