We studied the nyctohemeral cortisol secretion rhythm and the cortisol response to 1-24 corticotropin during Ramadan in 11 healthy, male volunteers aged 20-35 years. Their response to 250 mg 1-24 corticotropin was investigated 2 weeks before Ramadan by testing daily at 08:00 and 20:00 hours. After 16-22 days of fasting, their cortisol levels were measured at 08:00 hours and their response to 1-24 corticotropin at 20:00 hours. Before Ramadan, the baseline cortisol level was significantly higher at 08:00 hours than at 20:00 hours and the cortisol response to 1-24 corticotropin was also higher at 08:00 hours but this difference was not significant. During Ramadan, the cortisol level at 08:00 hours was lower than at the same time before Ramadan; the level at 20:00 hours was slightly higher than at the same time before Ramadan. There was no significant difference between the cortisol response to 1-24 corticotropin at 20:00 hours during Ramadan and the responses before Ramadan at 20:00 hours and 08:00 hours.