Locomotor activity of rat offspring sired by fathers treated with 0, 2 or 3 g/kg of alcohol twice daily was assessed at 21, 42 and 90 days of age. Fathers treated with the two lower doses were pair-fed to those treated with the highest dose. Offspring of nontreated ad-lib fed fathers were also evaluated to determine the possible role of paternal stress associated with intubation and pair-feeding. The behavioral response to amphetamine was also examined in 90-day-old male offspring. Paternal alcohol treatment resulted in increased activity at each age for 3 g/kg offspring compared to pair-fed controls. Ad-lib offspring did not differ from 0 g/kg controls at 21 and 42 days of age. The significant effect of paternal alcohol treatment on offspring activity at 90 days, including a significant linear paternal effect, occurred when all amphetamine-treated groups were pooled. The alcohol x amphetamine interaction was not significant, but a significant linear paternal alcohol x linear amphetamine interaction indicated that the paternal alcohol effect on activity was differentially responsive to amphetamine. Subsequent analysis of this interaction indicated a significant linear paternal alcohol trend only at the high dose of amphetamine. These results corroborate a previous report of increased activity on the part of offspring sired by fathers treated with alcohol. The presence of a differential effect of amphetamine suggests that the paternal effect on activity may be mediated by catecholaminergic activity. The absence of significant differences between ad lib and 0 g/kg pair-fed controls indicates that paternal stress/undernutrition does not significantly affect offspring activity.