Isolated, short-circuited [cow] rumen epithelium was used to study the effects of pH, concentration gradient, imidazole vs. bicarbonate-buffer systems, and fatty acid metabolism on the transport of volatile fatty acid. Transport of acetate and butyrate increased with an increase in concentration gradient or a decrease in lumen bath pH, and acetate transport also was greater when a bicarbonate buffer was used in place of imidazole. The two buffer systems also differed in their effect on short-circuit current and, therefore, the active transport of ions. Acetate, propionate, and butyrate were all metabolized to a considerable extent by the tissue but their metabolism was not a simple function of the amount of fatty acid absorbed. The results, including the effect of anoxia, indicated that this metabolism played a critical role in determining the rate at which these fatty acids were absorbed and transported by rumen epithelium.