A range of potent immunoregulatory molecules termed cytokines has become available for the therapy of human melanoma. Among the cytokines, the interferons (IFN) have been examined in great depth for the therapy of melanoma. IFN are able to modulate host effector cell function, including the tumor cytolytic function of lymphocytes and monocytes. IFN also have the capacity to regulate the distribution of circulating immunoregulatory (T) lymphocytes and the expression of tumor cell surface antigens, as well as class I and II products of the major histocompatibility locus. These activities of the IFN have led to their early application for treatment of human melanoma. The empirical evidence that IFN alpha exerts clinically significant anti-tumor effects against melanoma is reviewed, and evolving status of adjuvant trials of IFN alpha and gamma is noted. New indirect host-mediated anti-tumor activities that may potentially be manifest by IFN have yet to be fully harnessed. The opportunity to obtain meaningful anti-tumor activity in advanced disease or adjuvant settings, at dose ranges below those which are toxic (conventional maximal tolerable), are at hand. The U.S. cooperative groups [Eastern Cooperative Oncology Group (ECOG), Cancer and Leukemia Group B (CALGB), and South West Oncology Group (SWOG)] are studying IFN gamma in pursuit of this goal in advanced and adjuvant settings for melanoma and other tumors. The determination of the clinical role of IFN as biologic response modifiers demands equal commitment to the clinical assessment of immunobiologic mechanisms and anti-tumor effects. The immunologic assessment of IFN and a number of other cytokines is a major focus of the Pittsburgh Cancer Institute. Regional delivery of cytokines such as interleukin-2 (IL-2) may be the most appropriate and least toxic approach, given their half-life. Regional therapy by the intralesional route has yielded enhanced activity for a range of biologics, including bacillus Calmette-Guerin (BCG), IL-2, and tumor necrosis factor (TNF). Intralymphatic therapy with methanol extraction residue of BCG (MER-BCG) has been tested, and trials are now in progress with IL-2 to assess the optimal dosage by this route. It is likely that the optimal role of IFN and other cytokines will be found in combination with one another, and with different biologic modalities such as monoclonal antibodies and vaccines, to allow expansion and heightened activity of the desired effector cell populations in the host. Enhanced host toxicities, as well as anti-tumor effects, may require that special attention be devoted to optimal sequence of administration to enhance the therapeutic index.