Circulating levels of adrenalin, noradrenalin, cortisol and immunoreactive insulin were assayed in a group of supine, convalescent patients, at 2-h intervals during a period of 24 h. Circadian variation was demonstrated in both catecholamines and in cortisol. In all three factors, levels were higher during the day than during the night, but each showed a different periodicity. The amplitudes of the individual responses showed a positive correlation with the individual 24-h mean values in both catecholamines, but not in cortisol. The concentrations of adrenalin and noradrenalin recorded were consistent with the presence of some stress in the patients. Immunoreactive insulin responses to food stimulus were greater in the morning than in the evening, but the latter response was more prolonged. The implications of these results in continuous assessment of ill patients is discussed.