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Cancer vaccines represent a promising new strategy for immunotherapy against cancer, but their effects are insufficiently understood. The effect of heat treatment against mouse colon adenocarcinoma cell line (colon-26), and combined effects of heat treatment and immunizing host animals with heat treated colon-26 cell extracts were investigated. Heat treatment of colon-26 cells induced heat-shock protein 70 (HSP70), but not other HSP. Immunization of BALB/cJ mice with heat treated colon-26 cell extract, which was enriched in HSP70, elicited antitumour immunity against subcutaneously injected colon-26 cells. Furthermore, combination therapy of heat treatment and immunization with heat treated colon-26 cell extract significantly reduced tumour volumes compared with heat treatment alone. Similar immunization enhanced the cytotoxic activity of mouse splenic lymphocytes against untreated and heat treated colon-26 cells in an in vitro assay, as well as against heat treated allogenic mouse lymphoma cell line (YAC1). These findings suggest possible usefulness of heat treated cancer cell extract as a cancer vaccine, especially if given in combination with hyperthermia. [ABSTRACT FROM AUTHOR]