Gamma-hydroxybutyric acid (GHB) has been shown to reduce ethanol consumption and suppress ethanol withdrawal syndrome both in laboratory animals and humans. The present study was designed to assess the similarity between the discriminative stimulus effects, or subjective feelings, of GHB and ethanol using a T-maze, food-reinforced drug discrimination procedure. Three groups of rats were trained to discriminate ethanol (1.0 or 2.0 g/kg; p.o.) or GHB (300 mg/kg; p.o.) from water. In the 1.0 g/kg ethanol-trained rats, substitution for ethanol was an inverted U-shape function of GHB dose, with only 300 mg/kg GHB resulting in complete substitution for ethanol. No dose of GHB elicited selection of ethanol-appropriate arm higher than 10% in the 2.0 g/kg ethanol-trained group. In the 300 mg/kg GHB-trained rats, complete substitution for GHB occurred only at the dose of 1.0 g/kg ethanol. Doses of ethanol lower or higher than 1.0 g/kg did not substitute for GHB. The results of the present study indicate that symmetrical generalization between ethanol and GHB occurred within narrow dose ranges. They are discussed in terms of common neurotransmitter systems involved in the mediation of GHB and ethanol effects.