The effects of low to moderate doses of ethanol on spontaneous locomotor activity were studied in the selectively bred high-ethanol drinking (UChB) and the low-ethanol drinking (UChA) strain of rats. Alcohol-naive rats had food and water available ad libitum, although food was removed 24 hours before and during activity testing. After an injection of c.15 M NaCl or ethanol (0.25-1.0 g/kg), spontaneous locomotor activity was monitored every 5 minutes for 20 minutes in an open field apparatus. The UChB rats exhibited increased locomotor activity after doses of 0.25 and 0.50 g/kg of ethanol, while UChA rats failed to show increased locomotor activity at any ethanol dose. Moreover, the UChA rats appeared to be more sensitive to the sedating effects of 1.0 g/kg of ethanol than the UChB rats. These differences were not the result of different brain-blood alcohol levels. Ethanol intakes by the UChB and UChA rats determined at the conclusion of activity testing averaged 5.0 ± 0.5 and 1.9 ± 0.4 g/kg/day, respectively. The data suggest that ethanol-induced locomotor stimulation may be associated with ethanol preference and that hyperactivity may be an expression of the positive reinforcing effect of ethanol in UChB rats.