The proteinase inhibitor alpha 1-antichymotrypsin is present in the epithelial, stromal and endothelial layers of the human cornea. This was determined by immunolocalization in corneal sections and by Western blot analysis of extracts from the three separated layers. The inhibitor was quantified in the extracts by immunodot blot analysis. The levels observed were 1.3 +/- 0.3 microgram/cornea for the epithelial layer, 22.8 +/- 3.8 micrograms/cornea for the stromal layer and an average of 0.17 micrograms/cornea for the endothelial layer. alpha 1-Antichymotrypsin is being synthesized by the cornea. Metabolically labeled inhibitor was immunoprecipitated from the three layers following organ culture of the intact cornea. Two major forms were detected. These were the native, mature 64 kDa form and a 50 kDa form which is either a degradation product or an incompletely glycosylated form. These results indicate that the cornea has the ability to locally control degradation through synthesis of this inhibitor. Local synthesis of this inhibitor releases the cornea from total dependance upon the vascular system for its supply of alpha 1-antichymotrypsin.