Laboratory experiments were carried out to study the effects of cationic surfactant cetyltrimethylammonium chloride (CTAC) on the uptake of pyrene by fish gills. The uptake (including adsorption) of pyrene by gills of the color carp (C. carpio var. color) exposed to 20-100 microg/L pyrene in the presence or absence of 0.2-1.0 mg/L CTAC were determined. The sorption of pyrene by mucus was preliminary studied using a four-step sequential extraction procedure. Fish gills were extracted with H2O, 0.01 M CaCl2, CH3OH and a mixture of 1:1 n-C6H14/CH2Cl2 in sequence. Results showed that pyrene mostly accumulated in mucus and on the surface of gills tissue; the cationic surfactant CTAC significantly enhanced these accumulation or adsorption on the fish gills (not in gills). CTAC could affect the bioavailability ofpyrene in aquatic systems.