1. Wheat-bound residues of 14C-pirimiphos-methyl were fed to albino rats at 1.17 and 7.5 ppm in the diet for 3.5 months. 2. In toxicological tests, 1.17 ppm of bound residues caused an increase of rat alkaline phosphatase activity and blood urea nitrogen, and reduction in lymphocyte and monocyte counts. A dietary level of 7.5 ppm showed a significant decrease in serum cholinesterase activity and in lymphocytes and monocytes, and an increase in alkaline phosphatase activity and of urea nitrogen. 3. Bioavailability data indicate that wheat-bound pirimiphos-methyl residues are absorbed by rat.