Effects of light sources of different wavelengths, temperature, and pH values on the breakdown of 14C-azinphosmethyl in water or on glass surfaces were investigated. Primarily UV light (2537A) and to a lesser extent sunlight, degraded the insecticide to chloroform and water-soluble, compounds, while the products from yellow (5889A) and red (6563A) light radiation were similar to those from non irradiated controls, With 2-dimensional thin-layer chromatography, autoradiography, and selective color producing reagents, benzazimide, anthranilic acid, methyl benzimide sulfide, and X-methyl bemazimide were identified as chloroform-soluble irradiation products and 1 unidentified compounds were found to he water soluble. None of these was toxic to insects. A rapid degradation of the insecticide occurred only above 37¼, and to a greater extent in water than on a glass surface. Chloroform-soluble breakdown products were methyl benzazimide sulfide. N-methyl bemazimide, and bemazimide, and traces of merecaptomethyl bemazimide and the oxygen analogue of azinphosmethyl. Six unidentified water-soluble compounds also were isolated. The insecticide was relatively stble in water below pH 10. At pH 11, crloroform-soluble azinphosmethyl metabolites were primarily methyl bemazimide sulfide and bemazimide; however, the water phase contained 97.7% of the applied radiocarbon after chloroform extraction. Analyses of this extracted water indicated the presence of anthranilic acid and benzaizmide and 3 unidentified compounds.