Five groups of 400 hatchery rainbow trout, (Salmo gairdneri), were stocked in a small, mountain stream at )-week intervals from June to September, 1972. A fish trap captured any fish moving out of a 500 m study section. Fish began moving at high levels during the first day of each stocking and continued at high rates for 5-8 days (Early Phase), after which movement decreased to low levels for 6-9 days (Late Phase). Early Phase fish moved primarily at night, possibly due to their disoriented state and high subjectivity to stream conditions. Fish moving during Late Phase did so mainly during daylight, probably in response to diurnal periodicity of a day-active food organism in the drift. Forced movement due to social behavior did not seem to be an influencing factor, but the duration of visible light seemed important to moving fish.