It has been suggested that certain antitumor agents stimulate antitumor immunity. In the present study, we examined whether cisplatin and 5-fluorouracil (5-FU) accelerate the antitumor host responses in head and neck cancer patients. Two groups of patients were studied, i,e. an untreated (UT) group and a treated, disease-free (TDF) group that received chemo-immunotherapy in combination with radiotherapy and operation. When peripheral blood mononuclear cells (PBMC) derived from head and neck cancer patients were treated with cisplatin or with 5-FU, interferon-gamma, tumor necrosis factor (TNF)-alpha, TNF-beta, interleukin (IL)-1 beta, IL-6, IL-12 and IL-18 as well as killer cell activities were significantly induced in both groups. In this case, these activities induced by cisplatin in UT showed lower levels than those in TDF, whereas the activities induced by 5-FU in the UT group demonstrated almost similar levels to those in TDF. These activities were significantly inhibited by anti-asialo-GM(1) antibody. Furthermore, cytokine levels in sera and killer activities of PBMC derived from the cancer patients were significantly increased after cisplatin administration. These findings suggest that cisplatin and 5-FU increase anticancer immunity mediated by induction of cytokines and killer cell activities in patients with head and neck cancer. [(C) 2000 Lippincott Williams & Wilkins.].