We examined the effects of misonidazole (MISO) and recombinant human tumour necrosis factor (rh-TNF) on tumour blood flow in mice given hyperthermic treatments. MISO (500 mg kg-1) or rh-TNF (6 x 10(4) unit kg-1) was administered intraperitoneally (i.p.) prior to hyperthermia to nude mice bearing a xenoplanted human gastric cancer and tumour blood flow was measured by a hydrogen diffusion method based on polarographic determinations. MISO plus hyperthermia produced a temperature-dependent decrease in blood flow and, at 43.5 degrees C, the flow decreased to 15-30% of control and remained low for up to 24 h. Blood flow following rh-TNF plus hyperthermia was less than that at the same temperatures following MISO plus hyperthermia, and, at 43.5 degrees C, the flow decreased to 10-20% of control and remained low for up to 48 h. Tumour growth delay was closely related to the duration of the decrease in blood flow. Thus, the profound decrease in tumour blood flow following hyperthermia plus MISO or rh-TNF and the consequential tumour regression may well be of potential clinical significance.