ALKYLATING agents have been used in the Ltreatment of neoplastic disease since 1931, when Adair and Bagg1 described experiences with topical application of sulfur mustard. Intensive investigation during World War II resulted in a greater appreciation of the usefulness of these compounds. Pharmacological studies of mechlorethamine (methyl-bis [β-chloroethyl] amine) hydrochloride have been conducted almost entirely with biological tests, relying upon the lethality of the agent in the experimental animal to indicate potency. Recently, a colorimetric chemical determination has been developed2 by which it is possible to quantitate the presence of alkylating agents in aqueous biological media. With this test, many aspects of the basic reactions of mechlorethamine have been studied in order to confirm or repudiate concepts established by less accurate techniques. To gain knowledge as to the final applicability of the alkylating agent test and to determine its potential importance regarding the testing of new alkylating substances