During the coming year, we plan to examine the transport of two additional water-soluble vitamins: nicotinic acid and pyridoxine. The only adequate study on nicotinic acid absorption was performed on bullfrog intestine. An active transport process was implicated but the details of the process were not clarified. An in-depth investigation of the influx of nicotinic acid in mammalian intestine appears to be worthwhile. The results of three previous studies on pyridoxine transport have indicated that intestinal absorption proceeds by simple diffusion. However, because this vitamin is highly water soluble and because it is absorbed quite quickly through the mucosa, it would not appear that sufficient absorption would occur by the process alone. Thus, we plan to investigate the properties of pyridoxine influx at the brush border membrane. We will specifically test for saturation kinetics, metabolic dependence, sodium dependence and competition with influx of other vitamins.