The upstream orientation and frequency of upstream movement of ripe male rainbow trout (Salmo gairdneri) in the presence of ovarian fluid obtained from spawning females of the same species were observed and quantified. In a stream tank, male trout moved upstream in the ovarian fluid odor plume. In an optomotor tank, male trout exhibited an increase in the frequency of upstream orientation and movement in the presence of diffuse, nondirectional ovarian fluid. It is concluded that water currents provide directional cues and olfactory stimuli regulate the orientational and kinetic components of the rheotropic response. The significance of this mechanism of orientation in fish migration is discussed.Key words: rheotropism, behavior, olfaction, orientation, migration, ovarian fluid