The effects of ethanol-d6 on the lipid matrix of rat brain neuronal membranes were investigated by delayed Fourier transform 1H-NMR techniques. At 24 degrees C, neither 0.1 nor 0.2% (v/v) ethanol-d6 measurably affected the methylene resonance intensity. However, 0.4 and 1.0% ethanol-d6 increased resonance intensity, 35 and 51%, respectively. With increasing temperature, a decrease in resonance intensity for 0.1% ethanol-d6 was observed reaching a maximum of 20% at 42 degrees C. Furthermore, increasing temperature attenuated the increases in resonance intensity seen with 0.4 and 1.0% ethanol-d6. At 24 degrees C, no concentration of ethanol-d6 had a significant effect on the choline methyl resonance. However, with increasing temperature both 0.1 and 0.2% ethanol-d6 decreased this resonance's intensity. The intensity of the terminal methyl resonance was increased in a dose related fashion by ethanol-d6, reaching a maximum of +41% at 1.0% (24 degrees C). Increasing temperature attenuated this effect, but no concentration of ethanol-d6 significantly decreased resonance intensity. The increases and decreases in resonance intensity induced by ethanol-d6 are interpreted in terms of a decrease and an increase in membrane order, respectively. It is proposed that ethanol-d6 exerts two effects on neuronal membranes, an ordering effect on the membrane surface and a disordering effect in the membrane interior. A higher enthalpy of ethanol binding to the surface as compared to the interior of the membrane leads to an attenuation of the ethanol disordering effect with increasing temperature.