It has been suggested that the trabecular meshwork may be involved in the pathogenesis of open-angle glaucoma, and some authors have pointed out that disorders of the extracellular matrix components may play a role; nevertheless, nothing is known about the normal metabolism of connective tissue molecules in this particular tissue. We recently initiated some studies in this field and have focused on the in vitro effects of aqueous humor on collagen metabolism. We report the finding of a latent collagenase of low molecular weight in aqueous humor obtained from cataractous patients; the enzyme was identified through several methods, including its in vitro activity against radiolabelled type I collagen and additionally with a zymogram technique. It was partially characterized by high-performance liquid chromatography.