The effect of a deficiency of ascorbic acid (AsA) on in-vivo testosterone production in mature male rats was investigated using a mutant strain of rats (ODS rats) unable to synthesize AsA. Male 60-day-old rats were fed AsA-deficient lab chow for 28 days with [ODS(+)] or without [ODS(-)] AsA supply. The AsA levels in the liver of ODS(-) rats were undetectable and those in the testes decreased to about 25% of those in ODS(+) rats by day 28. Plasma LH levels in ODS(-) rats decreased to about 30% of those in ODS(+) rats by day 28. However, there were no significant differences in the plasma levels of testosterone, or in the relative weights of seminal vesicles and ventral prostates between ODS(+) and ODS(-) rats. Plasma levels of testosterone in ODS(-) rats after a single injection of 200 IU hCG changed similarly to that in ODS(+) rats. The metabolic clearance rate of testosterone was also the same at 60 min after an intravenous injection of [3H]testosterone in both groups. These results indicate that AsA-deficiency in adult rats causes no significant change in basal plasma levels of testosterone or in the response to hCG, despite decreased plasma LH levels.