Both hyperthermia and glutathione depletion have been shown to increase the antineoplastic activity of melphalan. Investigations were carried out to define the toxicity and activity of melphalan given in conjunction with local (right hind limb) hyperthermia and L-buthionine-SR-sulphoximine (BSO)-mediated glutathione depletion to athymic mice bearing the melphalan-resistant human rhabdomyosarcoma xenograft TE-671 MR. Administration of 0.5 of the 10% lethal dose of melphalan to mice treated with BSO and hyperthermia (42 degrees C for 70 min) resulted in a 53% mortality rate. The mortality rates for mice treated with melphalan alone (2.5%), hyperthermia alone (0%), melphalan plus BSO (13.5%), melphalan plus hyperthermia (12.0%) and BSO plus hyperthermia (0%) were substantially lower than triple therapy. Histological examination of kidney, liver, colon, and small intestine sections taken from non-tumour-bearing animals revealed a marked increase in damage to the small intestine (cryptal necrosis and epithelial denudement) in animals receiving triple therapy compared with animals receiving any other treatment combination. Gavage administration of sterile water (1 ml twice a day) completely prevented mortality in animals receiving triple therapy. Treatment of tumour-bearing animals with triple therapy plus gavage demonstrated a statistically significant increase in tumour growth delay compared with animals receiving any other treatment combination.