Irradiation of ca. 1.0 M solutions of dimethylamine in carbon tetrachloride at 300 nm and 35°g ave IV.lV.A'.lV'-tetramethylmethanediamine (22 mol %), dimethylamine hydrochloride (32 mol %), and chloroform (25 mol %), plus lesser amounts of methylamine. Quantum yields at zero conversion were 4.7 mol einstein-1 for disappearance of dimethylamine, and 1.2, 1.1, and 1.2 for appearance of diamine, amine hydrochloride, and chloroform, respectively. Similar reactions of dimethylamine were observed in chloroform and , , -trichlorotoluene, but with longer irradiation times. Diamine formed in irradiations of dimethylamine in deuteriochloroform showed no deuterium incorporation. A mechanism involving photodissociation of an amine-halocarbon charge-transfer complex, followed by disproportionation and/or combinations of dimethylamine' radicals, and, finally, by aminal disproportionation is supported by control experiments, quantum yields, and the protochemistry of potential and actual intermediates. The 4:1 reaction stoichiometry of dimethylamine to diamine corresponds to ca. 88% of theoretical yield for production of diamine.