Biologicals and biological response modifiers (BRMs) represent a new class of agents for cancer therapy. Historically, there have been many attempts to stimulate the immune response with nonspecific immunomodulators in the form of bacterial extracts, viruses, and chemicals. Although these approaches have occasionally proven useful under defined conditions in experimental models, their extension to the clinic has been largely unsuccessful. Recent advances in molecular biology and hybridoma technology have made available genetically engineered lymphokines and cytokines, as well as monoclonal antibodies, as highly purified biologicals for cancer treatment. These agents may act directly on tumor cells and/or may act on the patient's own biological responses to induce an antitumor response. Selective defects in T-cell function have recently been identified in cancer patients and in patients with acquired immunodeficiency syndrome (AIDS). Simultaneously, the availability of gamma interferon (gamma-IF) and interleukin-2 (IL-2) may allow for the selective correction of these T-cell deficits, leading to restoration of the patient's immune responses and perhaps correction of the clinical syndromes. Preliminary data suggest that gamma-IF and IL-2 have in vitro activity on these T-cell defects, and the preliminary evidence that these agents have activity in vivo will be reviewed. Extensive trials are being conducted at the National Cancer Institute with monoclonal antibodies as anticancer agents. Animal model experiments have demonstrated considerable antitumor activity of immunoconjugates using monoclonal antibodies tied to toxins. Preliminary clinical results suggest that T-101 in leukemia and lymphoma and 9.2.27 in malignant melanoma may prove useful as specific reagents in the treatment of these disorders. While the antitumor effects with these antibodies have not been dramatic, our preliminary data in approximately 30 patients with leukemia, lymphoma, and melanoma clearly demonstrate the ability of intravenous monoclonal antibody to locate and specifically label tumor cells bearing the target antigens. It has been possible to localize antibody on the tumor cells in melanoma deposits that are barely visible in the skin. These data and radioimaging data suggest a future role for immunoconjugates as anticancer agents.