Abstract: In the present communication seven amides, five ureas, three 2-imidazolidinones, three hexahydro-2-pyrimidinones and four thiosemicarbazones, similar to niridazole were synthesized for antifertility evaluation. Preliminary Pharmacological results showed that 5-chloro-2-acetyl-thiophene thiosemicarbazone was effective in termination of early pregnancy in rats at a dose of 5 mg/Kg.