The effect of copper ion on arachidonic acid metabolism in the corneal epithelium was studied. Our results showed that when 3H-arachidonic acid (1 microCi/microgram) was incubated with homogenate of corneal epithelium at 37 degrees C for 45 min., three metabolites were formed. Metabolite A, the major metabolite, was identified as 12-HETE by HPLC and GC. An analysis with chiral phase HPLC revealed that metabolite A was a (R)-enantiomer. The production of 12(R)-HETE was stimulated by low concentrations of CuCl2 (< 0.1 mM) and inhibited by higher concentrations of CuCl2. Study on the biological activity of 12(R)-HETE showed that it could stimulate migration of endothelial cells in a concentration as low as 10 ng/ml. These results suggest that one of the effects of copper ion on the corneal neovascularization may be to regulate the level of 12(R)-HETE.