It has been observed in rats that the measured volume of distribution of thiocyanate is decreased by high plasma concentrations of thiocyanate, and that large doses of thiocyanate have a faster rate of disappearance from the plasma than does endogenous thiocyanate at normal concentrations. These observations are interpreted as results of (i) the saturation of thiocyanate-concentrating compartments, and (ii) the inability of the kidney tubule to reabsorb large amounts of filtered thiocyanate.