The photosensitized reduction of some 4-nitrosopyrazoles and 4- nitrosoimidazoles using titanium dioxide as a photocatalyst has been investigated. The photoreaction produces the corresponding 4-aminoazoles and assumes an initial electron transfer from the conduction band of the excited titanium dioxide to the nitroso compound, followed by hydrogen transfer from the solvent. The photoreduction reaction takes also place by irradiating nitrosoazoles in the presence of triethylamine in acetonitrile, pointing out the electron transfer also to occur from a ground state donor to the excited nitrosoazole.