Pertinent spectral features of 0,0-dimethyl 0-(2,4,5-trichlorophenyl)phosphorothioate have been assigned on the basis of comparison with the vibrational spectra of the 0,0-dimethyl-d6 analog, the P = O analog, the 0,0-dimethyl-d6 P = O analog, and by comparison with vibrational assignments for 0,0-dimethyl phosphorochloridothioate, 0,0-dimethyl-d6 phosphorochloridothioate, and 1-fluoro-2,4,5-trichlorobenzene.