1. 1,2-bis(β-chloroethylthio)ethane (SM1) has been characterized relative to methylbis(β-chloroethyl)amine (HN2) by studies of its toxicity and carcinostatic activity in mice and rats.

  2. On a molar basis, SM1 was one-eighth as toxic as HN2. Toxic effects of both mustards on lymphatic tissues and intestine were comparable.

  3. SM1 showed carcinostatic activity comparable to that of HN2 against the ascitic tumors and leukemias tested but a decreased activity against established solid tumors.

  4. Pretreatment of animals with SM1 or HN2 before tumor transplanting revealed that the carcinostatic activity within the organism was more prolonged, while gross symptoms of toxicity were less severe with SM1.

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Aided by research grants from the American Cancer Society (Institutional Grant No. 43F), the National Cancer Institute (No. C-2074), U.S. Public Health Service, and the Damon Runyon Memorial Foundation.

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