The behavioral teratogenicity of ethanol was studied in a laboratory model of the fetal alcohol syndrome. Pregnant rats were placed in one of three groups: Ethanol (4 g ethanol/kg intubated twice daily; Purina Chow ad lib.); Sucrose (7 g sucrose/kg intubated instead of ethanol; Untreated (no intubations; Purina Chow ad lib.). Ethanol offspring did not differ from either control group in neonatal body weight or developmental measures. On Day 35, 2 female offspring per litter were tested for reactivity to acoustic startle stimuli. Activity was measured during the pre-stimulus foreperiod and during inter-stimulus intervals. Ethanol pups displayed heightened startle reactivity in the absence of hyperactivity or disrupted habituation. These data indicate that ethanol in utero produces hyperreactivity in the absence of morphological, body weight or developmental abberations.