A series of amidoximes was prepared and evaluated for possible antitumor activity against L1210 leukemia. Three of the most active compounds in the L1210 system, formamidoxime, acetamidoxime, and 2-aminoacetamidoxime hydrochloride, were also active against P388 leukemia. Acetamidoxime was marginally active against Lewis lung carcinoma. The active amidoximes showed best activity against L1210 leukemia when given two times daily, 5 hours apart, for 8 days. Most of the amidoximes produced excessive central nervous system stimulation.