The lordosis behavior of male guinea pigs from inbred strains 2 and 13 was examined. Significantly more isolated gonadally intact males of strain 2 than strain 13 displayed lordosis. Castration did not decrease the display of lordosis. In castrated strain 2 males, those which showed lordosis did not have higher plasma androgen, estrone or estradiol levels than those which did not show lordosis. They also did not differ hormonally from ovariectomized strain 2 females even though strain 2 females never showed lordosis without hormone replacement. Although the lordosis shown by strain 2 males was not related to endogenous gonadal hormone levels, estradiol benzoate (EB) administration facilitated lordosis. EB had no clear effect on lordosis in strain 13 males. Progesterone after EB priming had no further facilitative effect in males of either strain. These results indicate that lordosis is more readily elicited from strain 2 than strain 13 males. Furthermore, lordosis in strain 2 males is not dependent upon gonadal hormones for its display although it is facilitated by EB (but not progesterone).