Effects of hyperthermia on heat shock protein expression, alkaline phosphatase activity and proliferation in human osteosarcoma cells. Hyperthermia can be used as a possible adjuvant therapy in treatment of cancer patients. In this study, the direct effect of hyperthermia on osteosarcoma derived cell lines HOS85, MG-63 and SaOS-2 was investigated. Heat shock at 42 degrees C inhibited proliferation significantly in all three cell lines tested. Furthermore a sub-lethal heat shock (42 degrees C, 1 h) decreases alkaline phosphatase activity, the absolute marker for osteoblast-like cells, in all of the three cell lines. Hsp70 was expressed constitutively and was found to be upregulated in a time-dependent manner; by up to 150% in Western blot analysis. The results of this study indicate that heat shock has an inhibitory effect on human osteosarcoma cells. These data suggest that hyperthermia has an anti-tumour effect on cancers of the bone and might, therefore, become an adjuvant treatment option.Copyright (c) 2006 John Wiley & Sons, Ltd.