Most of the accumulation of polychlorinated biphenyls (PCBs) over the food chain can be attributed to contaminant uptake from food. The effect of fatty acid absorption on net uptake and transport fluxes of a selection of 14 PCBs over the organismal gut epithelium has been determined in monolayers of the colon carcinoma cell line Caco-2 as a model system. The thermodynamic fugacity approach and the physiology of enterocyte lipid digestion are combined to investigate gastrointestinal absorption of polychlorinated biphenyls. The resistances of the subsequent transport steps from the apical compartment through the enterocytes to the basolateral compartment were quantified in terms of conductivity parameters. During uptake of PCBs into the enterocytes, the resistance of the aqueous diffusion barrier adjacent to the brush-border membrane is overcome for more than 99% by means of micellar transport. In the interior of the cells, the aquatic cytoplasm compartment also provides an important route of transport to the PCBs with up to three chlorine atoms, but the more hydrophobic PCBs are preferentially transported by triglyceride particles and lipoproteins. Calculated triolein/water partition coefficients, K(m), in general are higher than taurocholate micelle/water, dimyristoylphosphatidylcholine membrane/water and n- octanol/water partition coefficients, K(TC), K(DMPC), and K(ow), respectively. Calculations suggest that the correlation between log K(ow) and log K(tri) is nonlinear.