The reactions of α-aminoacetonitriles with isothiocyanates gave 1-cyanomethyl-1,3-disubstituted thioureas or 1,3-disubstituted 4-amino-4-imidazoline-2-thiones depending upon the reaction conditions. In the presence of polar organic solvents such as methanol the former products were easily cyclized to the latter. 1,3-Disubstituted 4-amino-4-imidazoline-2-thiones were autoxidized in methanol affording 1,3-disubstituted 5-imino-2-thiohydantoins.