Pregnant female rats and mice (18th day) received orally 10 mg/kg of 1-naphthyl-N-methyl-[14C]-carbamate (carbaryl), an anticholinesteratic drug. Animals were sacrificed 1, 5, 8, 24, 48, 72 and 960 h after administration and whole-body autoradiography was performed. Autoradiograms of the uterine cavity indicate a placental transfer and a foetal fixation of [14C] carbaryl metabolites. 14C-activity can be clearly seen in the foetus from the fifth hour; it persits till birth. We found 14C-activity in mice 60 h after birth. In both species there are some sites of accumulation in the foetal tissues, mainly in the eyes, central nervous system and liver.