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Summary.-Griseofulvin, an antibiotic used to treat dermatophytosis, was tested for carcinogenicity in mice, rats and hamsters. Three groups of mice and rats were given the drug in powdered diet in alternating 5-week periods for life, at dose levels of 3.000, 1-500 and 0-300 (mice) and 2.0%, 1-0% and 0-2% (rats). A group of mice and 3 groups of hamsters received continuous daily treatment for life with griseofulvin at 3-000, 1.5%, 0.300 and 0.1% dose levels respectively. A significant incidence of hepatic tumours was observed at the 2 higher treatment levels in mice. Also, statistically significant rates (P < 0.001 and/or P < 0.020) of thyroid tumours, indicating a dose-response, were recorded in male rats at the 2.00/ 1-0%0, and 0 2% dose levels, and in females at the 2.0°, and 1.0% dose levels. Hamsters did not develop neoplasms in response to treatment at any level.

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To assess their carcinogenic effects, the ethylnitrosourea (ENU) precursors, ethylurea and sodium nitrite, [were administered to pregnant hamsters as a single intragastic] dose on day 15 of gestation, or introduced into the cecum on day 14. Since sodium ascorbate (NaASC) inhibits the biosynthesis of nitrosamides, identical doses of the precursors were given concomitantly with NaASC. Progeny of mothers treater intragastrically developed significant incidences of neurogenic tumors of the peripheral nervous system, with a predominance in females. The concurrent administration of NaASC with ENU precursors prevented carcinogenic effects in the progency, whereas the simultaneous inoculation of the precursors into the cecum produced no carcinogenic effects in the offspring.