Lesions, inflammations, or degenerative insults of the human retina are accompanied by the release of proteolytic enzymes. Their deleterious effect may be enhanced by the release of free radicals. Ginkgo biloba extracts are known to exert protective influences against the action of free radicals, and this prompted us to ask whether the application of such extracts might protect retinal tissue against proteolytic damage. Eighteen adult rabbits were fed for 3 weeks (+/- 3 days) with 40 mg/kg of G. biloba extract (EGb 761) or a terpene-free fraction of this extract, dissolved in their drinking water. Twelve control rabbits received no G. biloba extract. The animals were then euthanatized and their retinae isolated. After appropriate enzymatic treatment, the tissue was dissociated and the number of isolated Müller cells counted as an indication of the strength of the proteolytic effects. There was a significant protective action of EGb 761: in an average control rabbit 5,200 cells per milligram retinal tissue were isolated; application of EGb 761 markedly reduced this number to 2,500 (terpene-free fraction; CP 205) or 3,050 (terpene-containing fraction). It is concluded that G. biloba extracts may have a significant therapeutic value in cases of retinal damage.