Thirty-six subjects were categorized as light social drinkers (LSD) and 36 as heavy social drinkers (HSD) on the basis of both biological criteria, gamma-glutamyl transferase (GGT) and the mean corpuscular volume (MCV) and by self-reports of drinking habits. This study examined the effects of alcohol (0.7 ml/kg) and of noise (75 dB(A] on learning and performance, in choice RT and in immediate memory tasks. Each subject was tested in two consecutive sessions (the time factor) under one of the following experimental conditions: (a) silence + placebo; (b) silence + alcohol; (c) noise + placebo; and (d) noise + alcohol. On immediate memory, there was a strong effect of time which interacted with 'drinker' category, suggesting that HSD subjects learn less rapidly than LSD. Time interacted also with state (sober or intoxicated), showing that learning might be impaired even by a moderate dose of alcohol. On the reaction time task no main effects were found but the time X drinker category interaction was significant; in session 1 LSD's RT were shorter than those of HSD. It is suggested that regular heavy drinking might affect the learning abilities of those who are not yet labelled as alcoholics.