1,2-Bis(sulfonyl)hydrazine derivatives, designed to generate several of the electrophilic species classically believed to be responsible for the alkylating (chloroethylating) and/or carbamoylating activities of the chloroethylnitrosoureas (CNUs), were compared with respect to the cross-linking and nicking of T7 DNA to that caused by 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU), and 1-(2-chloroethyl)-3-(4-trans-methylcyclohexyl)-1-nitrosourea (MeCCNU). In the case of BCNU, a large proportion of T7 DNA strand nicking was found to be due to the generation of 2-chloroethylamine, produced from the hydrolysis of 2-chloroethylisocyanate, in turn formed during the decomposition of the parental nitrosourea. 1,2-Bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine (compound 1) gave a greater yield of DNA cross-links than the CNUs. Compound 1, as well as its derivatives that were incapable of generating 2-chloroethylisocyanate, did not produce detectable levels of strand nicking, indicating that N7-alkylation of guanine did not occur to a significant extent with these agents. Since compound 1 and its derivatives are believed to generate chloronium and chloroethyldiazonium ions, it would appear that these species could not be significantly involved in the N7-alkylation of guanine caused by the CNUs. The relatively low level of N7-alkylation of guanine residues and the relatively high yield of cross-links generated by some of the 1,2-bis(sulfonyl)-1-(2-chloroethyl)hydrazine derivatives implies that they are more exclusive O6-guanine chloroethylating agents than the CNUs. O6-Guanine chloroethylation is believed to be the therapeutically relevant event produced by the CNUs; therefore, compound 1 derivatives represent promising new cancer chemotherapeutic agents, since they appear to generate lower quantities of therapeutically unimportant, yet carcinogenic lesions, and more of the therapeutically relevant O6-guanine chloroethylation than the CNUs.