The reaction of phosphorus pentaselenide with a number of alcohols has been studied. The predicted products, the dialkyldiselenophosphoric acids, were unstable. Derivatives were isolated as the potassium salts or as the chromium(III) complexes. When the salts of the acids were not isolated from the reaction mixture, different derivatives having bridged selenium atoms, viz. (RO)4P2Se4 and (RO)4P2Se5, were isolated. The properties of these compounds as measured using infrared, ultraviolet, n.m.r. spectroscopic and differential thermal analytical methods are reported.