A batch of eggs was exposed to a patterned sound continuously from day 12 to day 18 of incubation, while a control group was hatched in the quiet. In a postnatal test all chicks tended to creep toward a stationary sound source, but the experimental group showed a preference for the sound heard during incubation. In a second test the experimental chicks followed a moving model longer when it emitted the familiar sound than when it emitted a novel sound or no sound at all.