Jejunal absorption of acetate, propionate, and butyrate-the three predominant short chain fatty acids (SCFA's) in small and large intestinal contents-was studied in 5 volunteer subjects. A triple-lumen perfusion technique was employed; the test solutions were isotonic and contained 0, 5, 10, 25, 40, or 50 mm of a SCFA as the sodium salt. Intermittent secretion of small amounts of acetate and butyrate occurred during 3 of 15 control perfusion periods, and the concentrations measured in intestinal samples exceeded those reported for circulating plasma. The three SCFA's were absorbed rapidly and at equal rates. Absorption rates rose in apparently linear fashion with the mean concentration in the study segment (up to 20 mm) but reached saturation at the higher concentrations present in the mixing segment. Water and sodium absorption increased slightly during butyrate absorption. The flow rate of fasting intestinal contents did not increase during SCFA perfusion. SCFA's are readily absorbed and do not exert a diarrheogenic effect in the normal human jejunum.