The effect of experimental folacin deficiency on the uptake and distribution of radioactive folic acid in the rat was investigated. Less radioactivity was taken up by livers of deficient rats than controls 24 hours after intraperitoneal injection of [3H]-folic acid, although more radioactivity was incorporated by the brain and kidneys of deficient rats. The distribution of radioactivity among the three folacin-binding proteins of rat liver cytosol and the binding protein of mitochondria was also studied. In deficiency, very little radioactivity was incorporated into cytosol binding proteins I and II, while more radioactivity was incorporated into cytosol binding protein II and the mitochondrial binding protein. A decrease in the endogenous folacin associated with all protein-bound and free forms was seen in deficiency with the major decrease coming at the expense of unbound folacin, and cytosol binding protein I. This latter protein may have a primary storage role in the liver.