The reaction of tris (hydroxymethy1) phosphine with monosubstituted and unsymmetrically disubstituted ureas has been shown to produce tris (4-substituted ureidomethy1) phosphine oxides. The products were characterized by ir spectra, NMR spectra, and elemental analyses. The NMR spectrum for tris (4-phenylureidomethy1) phos-phine oxide showed a triplet for the NH attached to the phosphorus methylene, appearing at a higher field than ...