Numerous investigators have observed a depression of cell-mediated immunity in patients with carcinoma of the head and neck using a variety of in vitro and in vivo assays. This report presents the data obtained when a group of head and neck cancer patients were evaluated for reactivity in an in vitro lymphocyte blastogenesis assay using polyclonal mitogens and specific antigens, numbers of peripheral blood T-lymphocytes, and levels of circulating immune complexes. Such an immunological monitoring protocol revealed a depressed reactivity of the cancer patients in the lymphocyte blastogenesis assay when compared to normal age-matched controls. We also observed that 75% of these patients had circulating soluble immune complexes in their sera before and after therapy. These preliminary data indicate that further research is needed to examine the potential role of soluble immune complexes in modulating the host's immune response.