Interferons, glycoproteins originally investigated as antiviral agents, are now known to be active as anticancer agents, immune system modulators, and growth control regulators. For these reasons, interferons have definite and documented relevance to dermatologists. In regard to viral diseases, therapeutic trials in humans have shown promising results in herpes simplex infections, vaccinia, laryngeal papillomas, and condyloma acuminatum, as well as in rabies and hepatitis B. Pilot studies with interferon treatment of melanoma have been so promising that the American Cancer Society has selected this area to receive additional research support. Also, the antiproliferative effects of interferons have potential application to proliferative diseases such as psoriasis.