We used the miniature pig to evaluate the effect of ethanol ingestion on the hydrolysis of pteroylpolyglutamate and on the uptake of pteroylmonoglutamate (PteGlu) by the intestinal brush border membrane, processes that are required for folate absorption. After feeding ethanol or sucrose at 60% of calories for 11 mo, the uptake of PteGlu by jejunal brush-border-membrane vesicles was similar in both groups of animals. Jejunal brush border pteroylpolyglutamate hydrolase was decreased by one-half in the ethanol-fed group. Jejunal brush-border-membrane fluidity, measured by fluorescence polarization, was similar in both groups. Acute exposure of the jejunal vesicles to ethanol increased membrane fluidity and decreased hydrolase activity but had no effect on PteGlu transport. Inhibition of jejunal folate hydrolase by chronic exposure to ethanol may be an early effect in the pathogenesis of folate malabsorption and deficiency in chronic alcoholism.