Abstract Well-characterized fractions of the synthetic polysaccharide Ficoll have been chromatographed on columns of pearl-condensed agarose gels of concentrations between 2 and 8%. The results agree with the theory that the Ficoll is sterically excluded from the gel, which is made up of a random three-dimensional network of long fibers. The agarose fibers, which were estimated to be approx. 50 A in diameter, appear to contain 35–50 % water.