Most experimentally induced fevers are acute, usually lasting approximately six to twelve hours, and thus do not mimic chronic natural fevers, which can extend over several days or more. To produce a model of chronic natural fever we infused eight goats (Capra hircus) intravenously with 2ml of 2x10¹¹ cell walls of Staphylococcus aureus (S. aureus), for six days using osmotic infusion pumps (10 µl.h^-1), while measuring changes in body temperature, behavior and plasma cortisol concentration. Seven control animals were infused with sterile saline. Abdominal temperature-sensitive data loggers and osmotic infusion pumps were implanted under halothane anesthesia. To compare our new model with existing models of experimental fever, we also administered 2 ml bolus intravenous injections of 2x10¹¹ S. aureus cell walls, 0.1 µg.kg^-1 lipopolysaccharide (Escherichia coli, Serotype 0111:B4) and sterile saline, in random order, to six other goats. Bolus injection of lipopolysaccharide and S. aureus induced typical acute-phase responses, characterized by fevers lasting approximately six hours, sickness behavior and increased plasma cortisol concentration. Infusion of S. aureus evoked prolonged fevers, which lasted for approximately three days, starting on day four of infusion (ANOVA, P < 0.05), and did not disrupt the normal circadian rhythm of body temperature. However, pyrogen infusion did not cause plasma cortisol concentration to rise (ANOVA, P > 0.05), or the expression of sickness behavior. In conclusion, infusion of S. aureus produced a fever response resembling that of sustained natural fevers, but did not elicit the cortisol and behavioral responses that often are described clinically and during short-term experimental fevers.