It has been postulated that ethanol primarily targets nonparenchymal hepatic sinusoidal and perisinusoidal cells. In the current experimental study, we investigated the hypothesis that the earliest morphological alteration in the liver following a single administration of ethanol is a change of the diameter of sinusoidal endothelial fenestrae. The diameter of fenestrae in healthy humans is similar to the diameter in New Zealand White rabbits. Therefore, the effect of intravenous injection of 0.75 g/kg ethanol on the diameter of fenestrae was studied using transmission electron microscopy in New Zealand White rabbits. Ethanol concentration peaked at a toxicologically relevant level of 1.1 ± 0.10 g/l at 10 minutes after injection. Compared to control rabbits (103 ± 1.1 nm; n=8), the average diameter of fenestrae in ethanol-injected rabbits determined at 10 minutes after injection was significantly (p<0.01) smaller (96 ± 2.2 nm; n=5). Detailed analysis of distribution histograms of the diameters of fenestrae showed that the effect was highly homogeneous. The smaller diameter of sinusoidal endothelial fenestrae following acute ethanol intake may induce a fast impairment of microcirculatory exchanges between the sinusoidal lumen and the space of Disse. In conclusion, a decrease of the diameter of fenestrae as early as 10 minutes after ethanol administration is likely the earliest morphological alteration induced by ethanol in the liver and underscores the potential primary role of liver sinusoidal endothelial cells in alcoholic liver injury.