A simple micro-method for the determination of molecular weights of chondroitin sulphate has been developed. Columns of Sephadex G-200 and Sepharose 6B were calibrated with fractions of chondroitin sulphate, the molecular weights of which had been determined by independent methods. The use of the calibrated columns for determining the molecular weights and molecular-weight distributions of unknown samples of chondroitin sulphate by gel chromatography is described. The effects of variations in the ionic strength of the eluant were studied. For the average of duplicate determinations of the molecular weight (M w) the 95% confidence interval was M w±3%.