The adsorption, mobility, and microbiological degradation of polychlorinated biphenyls (PCBs) in soil materials were studied relative to land disposal. The mobility of Aroclors 1242 and 1254 and a used capacitor fluid were measured by the soil thin layer chromatography technique. PCBs were immobile in all soils when leached with aqueous solvents (water and landfill leachate); they were highly mobile in all soil materials when leached with organic solvents. The rate of adsorption of PCBs by soil materials was found to be rapid, with equilibrium conditions achieved in less than 8 hr. The adsorption process conformed to the Freundlich adsorption equation. PCBs were found to be strongly adsorbed by soil materials. The adsorption capacity and the mobility of PCBs were correlated to the organic carbon content and surface area of the respective soil materials. Microbial degradation of PCBs was studied using mixed cultures of PCB-degrading microorganisms. Aerobic degradation of water-soluble Aroclor 1242 was 92 percent complete within 20 hr and as high as 98 percent within 10 days. PCB isomers with less than four chlorines were degraded while those with four or more chlorines were not significantly degraded. Soil samples collected from field plots where PCB-contaminated sewage sludge was applied for 7 years were found to contain mainly high chlorine substituted isomers. The field samples confirmed the mode of microbial degradation found in the laboratory studies.