Because hydrostatic pressure can antagonize the behavioral effects of anesthetics in many organisms, we examined whether ethanol-induced immobility of the nematode Caenorhabditis elegans was antagonized by 100 ATA pressure. Nematode mobility was examined at pressures ranging from 1 ATA to 132 ATA, with and without increasing concentrations of ethanol (0-1 M). Pressure > 100 ATA alone inhibited movement of the nematode (EP50 = 111.5 +/- 0.6 ATA), as did increasing concentrations of ethanol (EC50 = 487 +/- 44 mM). Pressure and ethanol appeared to be additive, and not antagonistic. Because of previous results implicating glycine receptor antagonism as a mechanism of pressure reversal, and our current inability to observe significant behavioral effects of strychnine or glycine inhibition of high affinity strychnine binding, we suggest that an absence of glycine receptors in these organisms is the basis for a lack of pressure antagonism of ethanol immobility.