The time-course of changes in the effects of topical epinephrine on the aqueous flow and the coefficient of protein entry into the anterior chamber (k(in)) were determined in 12 normal human subjects. Before and after instillation of 1.25% epinephrine in one eye, protein concentration in the anterior chamber (Ca) was determined from aqueous flare intensity using the laser flare-cell meter, and aqueous flow rate was determined by fluorophotometry. The k(in) was calculated from the Ca, plasma protein concentration, and aqueous flow rate. A single instillation of epinephrine affected neither the Ca nor the aqueous flow rate significantly. The calculated value of the k(in) showed no significant changes at any time of determination, which implied that a single instillation of epinephrine is insufficient to affect the permeability of the blood-aqueous barrier to plasma protein in the normal human eye.