A series of hydrazine derivatives was tested for antineoplastic activity. Cyanoacetic acid hydrazide (I), cyanoacetic acid methylhydrazide (II) and N-thioamido-N'-cyano-acethylhydrazine (VI) appeared to be the most active agents against sarcoma 180, Ehrlich carcinoma and Nemeth Kellner lymphoma. The maximum tumor weight inhibition ranged from 70 to 90%. N, N'-bis-cyano-acethylhydrazine (IV) and N-isonicotinoyl-hydrazine (VIII) showed significant antitumor activity in Ehrlich carcinoma and Nemeth Kellner lymphoma systems. None of hydrazine derivatives were active against L1210 leukemia. The most active agents, I, II and VI were further evaluated in leukemia P388, melanoma B16, Lewis lung carcinoma and mammary carcinoma 16/C, and the agent VI was additionally tested in plasmacytoma MP26, colon carcinoma 26 abd Walker carcinosarcoma 256 systems. However, there was no effect with any agent or dose tested against any neoplasm.