Conditioned place preference (CPP) with both visual and tactile cues, hyperactivity, and stereotypies produced by d-amphetamine (1-10 mg/kg ip, single dose) were studied in CD-1 mice at 2, 3, and 4 weeks from birth. CPP was shown from the youngest age onward in female mice and from 3 weeks in male mice. Hyperactivity was much more pronounced in postweanlings (3 and 4 weeks) than in preweanlings. Stereotypies (at 3.3 and 10 mg/kg) occurred from the youngest age and tended to peak at 3 weeks.