A series of pentavalent phosphorus compounds containing the nitroxyl and/or aziridinyl moieties was evaluated for antitumor activity against P 388 and L 1210 lymphocytic leukemias, and compared to the clinical agent thio-TEPA (1). The compounds with the structures 5-13 were found to be active, with a T/C value greater than 125. The percent ILS was also determined.