This study analyzes the level of total and bound pirimiphos-methyl residues in treated wheat grain and its toxic effects on rats. Wheat grain was treated with [14C]pirimiphos-methyl of 16.36 mCi/mmol specific activity to determine the bioavailability of bound residues in rats. At the same time, grain was treated with nonlabeled pirimiphos-methyl as required to determine any possible toxic effects of bound residues in a subacute feeding study in rats. Two dose levels were used: 10 and 100 ppm (the former being the recommended dose level in practical treatment). Estimation of the type of residues was performed at intervals of 0, 30, 90, 120, 150, and 180 days. During and after the animal feeding study, changes in body weight gain, organ weight, cholinesterase activity, serum enzyme activity, and hematology were investigated. There is an indication that bound residues of the pesticide pirimiphos-methyl provoke toxic effects to some extent.