Several 2-(aminocarbonyl)-1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydr azi nes were synthesized and primarily evaluated for antitumor activity against the murine L1210 leukemia. All of the compounds tested were capable of producing "cures" of mice bearing this tumor. One of the most active agents of this class, 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)- 2(-)[[2-chloroethyl)-amino]carbonyl]hydrazine, was further evaluated against a spectrum of transplanted murine and human solid tumors. Pronounced activity was found against all of the tumors including the murine B16F10 melanoma, M109 lung carcinoma, M5076 reticulum cell sarcoma, and the human LX-1 lung carcinoma. The activities observed compared favorably with those of the established antitumor drugs, cyclophosphamide, mitomycin C, and the nitrosoureas, evaluated concomitantly.