The transcorneal determination of the rate of decay of intracamerally injected iodinated I 125 serum albumin gives an accurate measurement of the rate of aqueous humor formation. The duration of pentobarbital sodium anesthesia had no effect on permeability of the blood-aqueous humor barrier. The blood-aqueous humor barrier, however, did become more permeable to inulin labeled with radioactive carbon (14C) and dextran labeled with radioactive carbon (14C) as a function of elapsed time after the original placements of needles into the anterior chamber. A positive correlation was found between intraocular pressure and the rate of aqueous humor formation in short term experiments. In longer lasting experiments these functions were dissociated.