In this report I summarize recently reported studies which establish the existence of a previously undocumented diffusional pathway for plasma-derived proteins from the ciliary body stroma to the anterior chamber of the normal mammalian eye via the iris root. The data support the hypothesis that nearly all of the plasma-derived protein present in the aqueous humor of the anterior chamber arrives via this pathway, thus by-passing the posterior chamber. Additional studies suggest that some of the protein transported via the pathway is shunted directly into the trabecular meshwork and aqueous outflow pathways. Perfusion studies show how the perfused eyes were later immunohistochemically stained to reveal the distribution and qualitative amounts of serum albumin. These studies strongly suggest that the well-known "wash-out" effect, encountered in experimental studies of aqueous outflow, arises predominantly from wash-out of the protein depot that serves as the anterior diffusional pathway for proteins. Taken as a whole, these studies support the hypothesis that protein is a physiologically relevant and important element in the generation of normal aqueous outflow resistance, possibly more important than glycosaminoglycans (GAG's).