Wheat grains were treated with14C‐pirimiphos‐methyl to generate bound residues for testing their bioavailability to rats. Bound residues accounted for 25% of the applied dose (50 ppm) at the end of one year. When the grain bound residues were fed to rats for 48 hours the animals eliminated 30 and 40% of the administered dose in urine and feces respectively, after 5 days. Radioactivity in some selected organs and blood accounted for 37% of the administered dose after 2 days, which gradually declined to17.after 5 days. These data indicate that wheat‐bound pirimiphos‐methyl residues are moderately bioavailable to rats. In a 90‐day feeding study, inhibition of plasma cholinesterase and brain acetylcholinesterase strongly suggest that the bound residues possess a toxicological potential.