This review presents the results of the clinical use of human leukocyte interferon (HLI) in certain diseases with viral etiology. Viral infections with manifestations in the eye, skin, and/or mucous membranes and in the respiratory system were treated with HLI by local application. HLI was incorporated into ointment, oil suspension, powder, dilution for inhalation, and dilution for subcutaneous and subconjunctival injections. The treatment in some of the diseases yielded statistical results that were highly significant in favor of interferon.