The present experiment investigates the activation of aggressive and sexual behaviors by gonadal hormones in female rats of the S3-strain. In the first experiment three doses of testosterone propionate (TP) were chronically injected. In the second experiment effects of TP were compared to those of estradiol benzoate (EB) and methyltrienelone (R1881), a synthetic, unaromatizable androgen. Females of the S3-strain were tested against TP-treated female Wistar rats as opponents, and masculine and feminine sexual responses were assessed in the test for aggression as well as in separate tests with sexually active stimulus animals. The results of the first experiment indicate that TP in all doses, increased aggressive as well as sexual behavior equally, although plasma testosterone levels differed significantly between the groups. In the second experiment, EB significantly decreased overall aggression as compared to control-treatment. TP- and R1881-stimulated fighting, particularly, as the most offensive parameter of aggression, but did not increase overall levels of aggression. Tests for sexual preference in which the choice between a sexually active male or female was given, indicated that TP-treated females stayed near males with longer durations. Scentmarking frequencies, measured in the semiopenfield test, were effectively activated by TP-treatment. EB- and R1881-treatment resulted in intermediate levels of marking behavior.