Subsequent treatment of diethylphosphonopropyl alpha-aminonitriles with 1,1'-carbonyldiimidazole or 1,1'-carbonyl-di(1,2,4-triazole) and hydrazines afforded substituted 3-amino-4-imino-imidazolidin-2-ones. Their acidic hydrolysis and their reactions with hydrogen sulfide are described. (C) 2004 Elsevier Ltd. All rights reserved.