Macromolecules in the pore fluid influence the mobility of hydrophobic compounds through soils. The study evaluated the significance of macromolecules in facilitating chemical transport under laboratory conditions. Partition coefficients between (14)C-labeled hexachlorobenzene and three macromolecules (dextran, humic acid, and groundwater dissolved organic carbon (DOC)) were determined in a three-phase (water-macromolecule-soil) system. There were significant differences between the macromolecule:water partition coefficients, which ranged from 1 X 10 sup 3 to 1 X 10 sup 6. Soil:water partitioning for humic acid was demonstrated by using column breakthrough curves where the breakthrough curve for humic acid was retarded behind (3)H2O. Breakthrough curves for dextran and groundwater DOC demonstrated apparent size exclusion, as these compounds eluted from the soil column before the (3)H2O. The impact of the dextran was demonstrated under dynamic conditions by use of hexachlorobenzene, anthracene, and pyrene with and without macromolecules in replicated, biologically inhibited (sodium azide), saturated soil columns. (Copyright (c) 1989 American Chemical Society.)