• The effects of alcohol on formal aspects of social communication were studied by scoring transcripts of verbal discussions between dyads in alcohol and placebo sessions. At a low dose (0.83 to 1.0 ml/kg), alcohol significantly (P <.01) increased the amount of and overlap in communications, and tended to decrease subjects' acknowledgement of their partners' statements. At a high dose (1.5 ml/kg), the rate of overlap in speech was additionally increased, but there was a leveling off or reversal of the drug's effect on amount of communication. The subjects' blood alcohol levels were not related to the drug's effect.