We examined the effects of gamma-hydroxy butyrate (GHB) alone and in combination with either ethanol or NCS 382 [(2E)-(5-hydroxy-5,7,8,9-tetrahydro-6H-benzo[a][7]annulen-6-ylidene], a purported antagonist at the GHB receptor. These effects were examined on the responding of rats under a fixed-ratio (FR) 10 schedule of sugar solution (14%, w/v; 0.1 ml) presentation. GHB dose-relatedly decreased responding. When GHB was combined with ethanol, the effects of the two drugs were less than additive. NCS 382 did not antagonize the rate-decreasing effects of GHB. These observations are consistent with the notion that many of the behavioral actions of exogenously administered GHB result from GHB's actions at sites other than the GHB receptor, and are inconsistent with the popular notion that the effects of GHB and ethanol are synergistic.