To determine whether the prevention of fever affects the survival of an animal infected with pathogenic bacteria, lizards (Dipsosaurus dorsalis) were infected with live Aeromonas hydrophila and received varying doses of sodium salicylate, an antipyretic drug. Twelve lizards received identical injections of bacteria along with a nontoxic dose of sodium salicylate; five animals increased their mean body temperature at least 0.6 degrees C and survived the week, whereas seven did not develop a fever and died within 3 days. These data indicate that in these lizards the prevention of fever by use of an antipyretic drug such as sodium salicylate increases the mortality rate from bacterial infection.