The goal of the proposed research is to explore the extent and mechanism of the antagonistic effect of low level hyperbaric environments on ethanol intoxication. Experiments will be conducted in C57 Bl/6j mice, BALB/cj mice and guinea pigs (Hartley) using sleep-time, rectal temperature, respiratory rate, mortality (LD50) and signs of tolerance and physical dependence as measures of the antagonistic interaction between ethanol and low-level hyperbaric environments. These experiments will: 1) Determine the generality of the antagonism across strains and species; 2) Investigate the extent of the antagonism including its ability to antagonize hypnotic and lethal ethanol doses and ethanol in combination with other drugs; 3) Outline the time-course of the antagonism; 4) Explore the mechanism of the antagonism by determining the possible involvement of central neurotransmitter systems in the antagonism and by investigating the effect of hyperbaric environments on the development of tolerance and physical dependence to ethanol. It is felt that these studies will provide further insights about the mechanism(s) by which ethanol affects the brain and behavior and may provide a useful ethanol antagonist.