Chemotherapy became the primary treatment for small cell lung cancer (SCLC) in the early 1970s. The standard drug combinations were first vincristine, adriamycin, and cyclophosphamide (VAC) and then, from the early 1980s, etoposide-platinum combinations. Despite a good initial objective response, however, patients usually suffer a rapid relapse. Treatment development has, therefore, focused on ways to overcome drug resistance, and on the addition of cytokines to the chemotherapeutic arsenal. Interferon (IFN) was one of the first cytokines found to have anticancer effects, and it was introduced into the combined modality regimens used to treat SCLC in the early 1980s in an attempt to overcome the problem of early relapse. The role of IFN was investigated with the aim of establishing how best to combine it with other treatments for SCLC. In this paper, we review the impact of IFN on the outcome for 714 SCLC patients who were treated in randomized IFN trials at one institution over a period of 20 years and IFN trials conducted at other institutions during the same period. The parameters we used at our institution to measure outcome tended to improve during the period when patients were being treated in our three randomized IFN trials, compared with the period when patients received only standard treatment in a nonclinical trial setting. However, the differences were not statistically significant. During this period, IFN was used as maintenance therapy, concomitantly with chemotherapy, and combined with other treatment modalities. Our experience is that IFN-alpha is most effective when administered as low-dose maintenance treatment. Other IFN trials published during the same period were small and heterogeneous. Results were inconsistent and added little new information, although it has been shown that high pretreatment levels of serum vascular endothelial growth factor (VEGF) predict a poor response to treatment and consequently a poor outcome. The recently confirmed antiangiogenic properties of IFN deserve to be investigated in studies of maintenance treatment, in combination with other biologic agents. Patient should be selected according to criteria based on pretreatment assessment of biologic markers, such as VEGF and basic fibroblast growth factor (bFGF). Our studies, all at one institution, pioneered the biologic treatment of solid tumors and developed a solid basis of knowledge for future studies of biologic agents in cancer treatment.