Susceptibility of guinea pigs to chemical carcinogens: 7,12-Dimethylbenz(a)anthracene and urethan.

4, 8, 16, 18, 23, 24, 27, 30, 31), benzopyrene (presumably 3,4-benzopyrene)(13, 14, 17, 18, 26, 33), and 1,2,5,6dibenzanthracene (16, 18, 21 , 25). The relatively poor response of guinea pigs to the stimuli of carcinogenic chemicals has been attributed to an inherent species resis tance. Such claims were primarily based on a number of observations that spontaneous neoplasms were less frequent in guinea pigs than in other laboratory animals. At the beginning, only a few, often single, cases of spontaneous tumors were reported to exist and were described at great length (1 , 11, 12). Later, however, the investigators pub lished their findings systemically and found more lesions (5, 9). The literature on this subject has been extensively reviewed from time to time (9, 22, 33). The present work is part of our integrated program in studying the influence of age in chemical carcinogenesis and is intended to investigate the susceptibility of guinea pigs to the development of tumors by single and repeated injections of DMBA and repeated injections of urethan.