Among interferon (IFN)-alpha, beta, gamma, there are no differences in its clinical effects and toxicities. As to IFN-alpha, there are leukocyte IFN, lymphoblastoid IFN, recombinant IFN-alpha 2a, 2b, and 2c. Now we have largely completed the process of surveying for anticancer effects over the broad range of malignancies. However, the adequate method of administration, route, dose, and interval are not yet fully established. Dose response remains unanswered question with some contradictory results in in vitro and clinical reports. The actual mechanism responsible for its anticancer activity is still not known. The question of what variables to monitor in assessing adequate dosages of IFN remains unsolved. Several trials have examined the possibility of combining IFN with other treatment modalities including anticancer agents, BRMs, radiation, etc. It should be acknowledged that we remain at a very early stage in our understanding of IFN. In future, IFN may play an even larger role when used in an adjuvant setting or as part of multimodality cancer treatment.