Salivary cortisol profiles (hourly sampling over a 16-hour period) of 10 patients with chronic fatigue syndrome (CFS) but without concurrent depressive disorder were compared with those of 10 healthy volunteers matched for age, sex and menstrual cycle. The mean saliva cortisol concentration over the 16-hour period was slightly but significantly greater in the patients than the controls (p < 0.05). These findings are at variance with earlier reports that CFS is a hypocortisolaemic state and suggest that in CFS the symptom of fatigue is not caused by hypocortisolaemia.