RDS-127, in a dose-related manner, induced seminal emission ex copula after intracerebroventricular (i.c.v.) administration. In mating tests initiated 6 min after i.c.v. administration, RDS-127 induced decreases in ejaculation latency and intromission frequency, with some rats ejaculating on the initial intromission. Additionally, penile reflexes were eliminated by 150 micrograms and 600 micrograms, but not by an intermediate dose. In in vitro radioligand binding studies, RDS-127 potently displaced [3H]DPAT binding to 5-HT1A sites in rat cortex (Ki = 14 +/- 4 nM) and was only moderately effective in displacing [3H]spiperone binding to dopaminergic D2 sites in rat striatum. RDS-127 was essentially ineffective at 5-HT1B sites labeled by [3H]5-HT in rat striatum (Ki = 13 000 +/- 4 000 nM). These data demonstrate that centrally administered RDS-127 mimics the previously reported alterations in sexual behavior after systemic treatment and that RDS-127 is a high affinity 5-HT1A agent with low affinity at the 5-HT1B binding site.