The metabolic fate of dichlorvos in swine has been studied by short- and long-term oral and inhalation exposure studies utilizing32P-,36Cl-, or14C-labeled dichlorvos. In dietary studies slowrelease formulations in PVC were used. No intact dichlorvos could be determined in the blood or tissues of treated animals, and, of the recognized metabolites, only dichloroethanol was found in measurable quantities under some conditions. Studies with36Cl-dichlorvos demonstrated that no organochlorine metabolic residues accumulated in tissues. The cumulative evidence from all studies indicates that the detoxification and degradation of dichlorvos in swine proceeds by essentially the same route whether the compound is administered orally or by inhalation exposure. This degradation proceeds almost exclusively via cleavage of the vinyl-phosphate bond and subsequent dechlorination of the dichlorovinyl product. Evidence is presented for the presence of a symmetrical two-carbon intermediate prior to the formation of glycine, an early metabolic product utilizing the vinyl carbons of the dichlorvos melocule. The isolation and identification of numerous14C-labeled normal biochemical cell constituents implies that further degradation proceeds via well-recognised metabolic pathways.