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Desorption of PCBs from sediment can significantly affect the ultimate fate and effects of PCBs in aquatic systems. Using a gas purging technique to strip soluble and sorbed polychlorinated biphenyls (PCBs) from solutions and sediment suspensions, Henry's law constants, approach to equilibrium, and desorption rate constants for four PCB congeners were measured. Henry's law constants were on the order of 10 −4 m 3 atm mole −1 . Desorption rate constants measured for a predominantly kaolinitic, low-organic carbon sediment were on the order of 0.03–0.1 days −1 . In contrast, desorption rate constants measured for a sediment composed of montmorillonite with a 3% organic carbon content were on the order of 0.009–0.04 days −1 . Desorption data suggest that equilibration times for PCBs with low chlorine content are on the order of six weeks, and months to years for PCBs with a significantly higher chlorine content.