Female rats acquire cocaine self-administration more rapidly than do males. There are also estrous cycle effects on cocaine self-administration, with females having greater cocaine self-administration during estrus relative to other days of the cycle. Previous work from this laboratory has demonstrated that acute estradiol administration in ovariectomized (OVX) females enhances the acquisition of cocaine self-administration and increases the amount of cocaine self-administered (Hu et al, SFN Abstr., 2002). These experiments were conducted to examine the activational effects of ovarian hormone administration on acquisition of cocaine self-administration in male and female rats. Six groups of adult Sprague Dawley rats were tested: OVX females treated with oil vehicle (OVX), OVX females treated with 5 µg estradiol benzoate (EB, OVX+E), OVX females treated with EB and 125 µg progesterone (E+P), castrated males treated with oil vehicle (Cast), castrated males treated with EB (Cast+E) and sham-castrated males tr...