Repeated treatment with 3-methylcholanthrene (MC; 25 mg/kg body weight, i.p., two times per week, 1 month) in both male and female Wistar rats resulted in decreased performance in two sessions of a two-way active avoidance procedure. In addition, young male rats that were injected repeatedly with MC prepubertally showed diminished acquisition in conditioned avoidance behavior during both sessions. It appears that MC can alter both avoidance acquisition and retention test performance in adult male and female rats, as well as in young males. This effect was not associated with alterations in sex hormone levels. The findings of this study suggest a significant influence of MC on specific mental functions.