Using bilateral injection into the anterior hypothalamic/preoptic region of the conscious, indomethacin pretreated cat as an assay system, the pyrogenic activity of two thromboxane A2-mimetics (SQ26655 and U46619) and thromboxane B2 was assessed. PGE2 was used as a reference pyrogenic agent. Thromboxane B2 and both of the thromboxane A2-mimetics were at least 5263 times less potent than PGE2. The results do not support the putative role of thromboxanes as mediators of fever.