Several recent publications have described the usefulness of high-resolution proton magnetic resonance (n.m.r.) for the elucidation of structure of phosphorus-containing organic compounds used as pesticides. Because phosphorus n.m.r. is playing an ever-increasing role in structure characterization and qualitative identification, of phosphorus compounds, the authors have examined (31)P n.m.r. spectra of a series of organophosphorus pesticidal compounds. Chemical shifts for thirty-seven organophosphorus pesticides have been measured and correlated with the structures of nine classes of these compounds. Empirical correlations describing the relative effects which the atoms adjacent to phosphorus have on the chemical shifts are given for some of these classes. These correlations between (31)P n.m.r. shifts and structure are presented for use in qualitative prediction.