Both in vitro and in vivo studies have demonstrated antiproliferative effects of interferon alfa-2b (Intron A; Schering-Plough) when tested with human tumor cells. A clonogenic assay has been widely used to determine its direct antiproliferative effects on human tumor cells in vitro using colony reduction as a reproducible endpoint. As a single agent, interferon alfa-2b shows maximum tumor cell colony reduction when used in high concentrations with continuous cell exposure. Short-term exposure to interferon alfa-2b does not produce significant tumor cell colony reduction. Clonogenic assays have also been used to test combinations of interferon alfa-2b with cytotoxic drugs. Variations in drug scheduling, sequencing and concentrations have indicated the best combinations which maximize tumor cell colony reduction. Combinations of interferon alfa-2b with doxorubicin, cisplatin, vinblastine, melphalan and cyclophosphamide have been shown to have at least additive and occasionally synergistic antiproliferative effects. In clinical trials, optimal pairs of agents have been identified frequently combining either doxorubicin, cisplatin or vinblastine with interferon alfa-2b. Pretreatment with interferon alfa-2b has been adopted from in vitro studies and applied to most clinical trials. One study has enrolled 135 patients having a variety of advanced or recurrent solid tumor types, using a schema which combines interferon alfa-2b and doxorubicin administration, both given on a weekly basis for three weeks, followed by treatments every two weeks in responding patients. Clinical responses have been seen using this regimen in patients with ovarian, cervical, colorectal and pancreatic carcinomas and in one lymphoma patient. Another study has been designed combining melphalan, prednisone and interferon alfa-2b for the treatment of patients with relapsing multiple myeloma. This is also based upon preclinical data. New methods of administration are being studied giving interferon alfa-2b as a single agent or in combination with cisplatin by the intraperitoneal route to patients with relapsing ovarian carcinomas limited to the peritoneal cavity. This method can maximize both the levels of interferon alfa-2b as well as the tumor cell exposure time.