Radical intermediates formed during irradiation of selenides and diselenides have been trapped by using nitrosodurene. ESR spectra show that, depending upon the organoselenium compound used, the radical species results from the cleavage of either a C—Se bond or a Se-Se bond. The hyperfine coupling with ⁷⁷Se has been detected for RSeN(O)R', and indicates a low spin density on the selenium.