Administration of endotoxin suppresses circulating concentration of luteinizing hormone (LH) in a number of species, including rats, sheep, cattle, and non-human primates. Specifically, endotoxin administration decreases circulating concentration of LH and LH pulses frequency in castrated male sheep. Endotoxin could alter circulating concentrations of LH via actions at the hypothalamus through altered GnRH production and/or release, or endotoxin could alter circulating concentrations of LH at the level of the pituitary via inhibition of LH production and release or inhibition of LH in response to GnRH. The site of endotoxin suppression of circulating concentrations of LH as well as possible mediators of endotoxin suppression of circulating concentrations of LH, including cortiocotropin-releasing hormone, arginine vasopressin, glucocorticoids, inflammatory cytokines, prostaglandins, and opioids, are discussed.