The effects of low concentration of lead acetate on the apical surface of the jejunal enterocytes were studied. Young male rats were divided into 2 groups which received 0.01% lead acetate solution in drinking water during 30 and 60 d respectively. Blood lead concentrations of poisoned rats were elevated to 30.33 micrograms Pb/100 ml at d 30 of intoxication, then slightly depressed at the end of experiment. Weight gain was impaired only in the 60-d group in comparison with controls. Samples from jejunum were processed for scanning electron microscopy using a critical point drying method and gold evaporation. The fine structure of the surface enterocytes was always determined in the epithelial bands above the levels of crypts nearly half a distance from crypt to villous top. The shape of the jejunal villi in poisoned rats was similar to that in non-poisoned rats. A marked feature of the rats' jejunum exposed to heavy metal for 30 d was a rough appearance of the surface villi, probably associated with distortion of the glycocalyx layer. Extensive areas with degenerative lesions were observed on the surface of the most villi on the 60th d of intoxication. Microvilli of enterocytes distributed within these areas were deformed and sometimes could be completely absent. All enterocytes exhibited various degrees of glycocalyx disturbance. It was concluded that the pronounced toxic effects of lead were related to modification of biochemical properties of the surface coat of enterocytes. This abnormal function of the glycocalyx could result in damage and microvillous malformations.