I examined downstream displacement of young-of-the-year fishes (primarilycentrarchids and cyprinids less than 25 mm total length, TL) by field sampling of drift duringfloods and by an experiment conducted in a 4.9-m-long artificial stream channel. The pattern ofdrift during a June 1985 flood (stage increase of 3.2 m) in Brier Creek, Oklahoma, indicated thatboth centrarchids and cyprinids smaller than 10 mm TL were extremely susceptible todownstream displacement. Drift rates of larger fish (10 25 mm) during both the June flood and asmaller flood (stage increase of 0.4 m) in July 1985 suggested that these fishes were much lesssusceptible to displacement. The rapid decline in susceptibility to displacement with increase insize from the field study coincided with results obtained in the artificial channel. These resultssuggest that the effects of floods on stream fish communities can depend on small differences inthe timing of reproduction and of flooding.