In a series of papers, Kinsey * developed the technique of posterior chamber taps and has applied this technique both to the study of steady-state relations between plasma and posterior and anterior chamber concentrations of normal constituents3 and to the analysis of aqueous humor dynamics as disclosed by the changing concentrations of a test substance in anterior and posterior chambers following the injection of such a test substance into the animal.4 To express the rate of change of concentration of the test substance in the anterior chamber, Kinsey and Palm have used the equation where Cπ, Ca, and Cp represent, respectively, the momentary concentrations of the test substance in the fluid passing through the pupil (π), in the anterior chamber (a) and in the plasma (p). Kf represents the rate of flow per minute as a fraction of the volume of anterior chamber; Kd