Cannabinoids have been shown to produce greater behavioral effects in female than in male rats. Sex differences in the metabolism of Delta(9)-tetrahydrocannabinol (Delta(9)-THC) have also been demonstrated in one study. The goal of this study was to determine if sex differences in Delta(9)-THC disposition or metabolism could explain sex differences in Delta(9)-THC-induced behavioral effects. [(3)H]-Delta(9)-THC was administered intraperitoneally (i.p.) to rats and the presence of [(3)H]-Delta(9)-THC and metabolites in serum and brain tissue were compared at multiple times post-injection in male versus female rats. Serum levels of Delta(9)-THC and its metabolites were similar in males and females. In brain tissue, [(3)H]-Delta(9)-THC levels also were similar in males and females. In contrast, levels of Delta(9)-THC metabolites in brain tissue, including 11-hydroxy-Delta(9)-THC, the major active metabolite, were higher in females than in males. To further investigate if greater production of active metabolites by females explained the greater Delta(9)-THC-induced behavioral effects observed in females, i.p. Delta(9)-THC-induced antinociception (50 degrees C warm water tail withdrawal assay) and catalepsy (bar test) were compared in male and female rats following pretreatment with saline or SKF525A, a cytochrome P450 inhibitor. SKF525A did not affect basal responding in the tail withdrawal assay or bar test in either sex. SKF525A significantly attenuated Delta(9)-THC-induced antinociception only in females. A similar sex difference was observed in the effects of SKF525A on Delta(9)-THC-induced catalepsy. These results suggest that the greater levels of active Delta(9)-THC metabolites produced by females contribute to greater behavioral effects of Delta(9)-THC in female compared to male rats.