Forty-five patients with virologically confirmed dendritic keratitis were treated in a randomized, double-blind controlled study with a basic therapy of trifluorothymidine (TFT) eye drops. In addition they received different human recombinant interferon (rHu IFN) eye drops. The following results were obtained for average healing times: TFT plus one drop daily of rHu IFN-alpha 2 arg (30 million iu/ml): 3.3 days, TFT plus rHu IFN-gamma (30 million iu/ml): 3.9 days, TFT plus a mixture of alpha plus gamma (0.3 million iu/ml each): 6.1 days, TFT plus a mixture of alpha plus gamma (1.5 million iu/ml each): 3.3 days. High-titer gamma interferon did not significantly differ from high-titer alpha interferon in the combination therapy of dendritic keratitis. A mixture of alpha plus gamma at a moderate titer (1.5 million iu/ml each) was as effective as a high-titer mono-preparation. Adding a low-titer interferon mixture gave no better therapeutic results than antiviral monotherapy. Thus it seems possible to save about 90% of interferon commonly used in the combination therapy of dendritic keratitis by applying a mixture of different suitable interferons instead of interferon monospecies.