The acute oral LD50 of N,N'-dicyclohexyl g-phenylenedismine for young, male albino rats is 1.07 (0.69-1.66) gm/kg, and that of N,N'-dioctyl g-phenylenedismine is 1.54 (1.06-2.23) gm/kg. The mean LD50 estimates are not significantly different at a level of probability of p = 0.05. Both of the above compounds, as well as N,N'-di-(g-methy1cyclobexyl) E-phenylenediamine were of about the same order of toxicity in single doses by mouth to male albino mice. Similarly, the LD50 estimates by single intraperitoneal injection to mice were comparable for the three products. In a test involving topical application to the depilated skin of male albino guinea pigs, the dicyclobexyl and dioctyl derivatives proved to be only slight primary irritants. However, with repeated application the dicyclohexyl derivative induced a somewhat greater degree of sensitisation than did the diocty1 derivative.