THE PRESENCE of lens epithelium on the anterior lenticular surface only has led to speculations concerning the possibility of posteroanterior nutrient flow through the lens. Besides the obvious physiologic importance of such a nutrient flow, there exist many pathologic implications—for example, it would be attractive to consider cataract as a sequel to metabolic or senile changes of the lens epithelium. In an attempt to demonstrate whether such a posteroanterior metabolic gradient exists, the concentration of radioactive phosphorus in different portions of the rabbit lens was studied by the following techniques. METHODS Adult albino rabbits were given radioactive phosphorus (P 32 ) intravenously in the form of acid phosphate. After the given time (see accompanying Table for dosage of P 32 and time allowed for absorption into lens) the eyes were enucleated, with local use of procaine anesthesia. Immediately after enucleation the lenses were removed without injury to the capsule, rinsed briefly