Lentil grains treated with malathion and stored under laboratory conditions for 12 months formed bound residues. Bioavailability and the effects of lentil‐bound residues of malathion in rats were studied. The amount of bound residues in lentils treated with14C‐malathion at 10 ppm and 50 ppm gradually increased to 9.52% and 13.01% of the initially applied doses after 12 months. When rats were fed these14C‐bound residues, radioactivity excreted in urine accounted for 34.49% of the administered dose. In feces, 26.15% of given dose was methanol‐extractable while 18.67% was determined as nonextractable. Various tissues including liver, kidney, fat and lungs contained 8.93% while radioactivity in expired air (14CO2) was low (1.51%). The results indicate that lentil‐bound malathion residues are highly bioavailable to rats. Analysis of the lentil material containing bound residues indicated that the main compound was malathion.