Sera from 85 patients with head and neck cancer including laryngeal cancer, hypopharyngeal cancer, nasopharyngeal cancer, and maxillary cancer were assayed for immune complexes (IC) by solid-phase anti-C3 enzyme immunoassay and for squamous cell carcinoma-related (SCC) antigen by radioimmunoassay. The positive rates of IC and SCC antigen in head and neck cancer patients were 29.4% and 34.1%, respectively. Their serum levels and positive rates were found to be elevated according to the degree of advancement of the disease stage, showing their good clinical correlations. With individual patients there was no significant relationship between IC and SCC antigen.