This investigation deals with the circadian rhythm (CR) of hunger sensation (HS) in obese patients before and after a four-week, moderately hypocaloric diet with a substitutive meal. The study was performed on 25 non-diabetic obese patients (5 males and 20 females, mean age: 39.7 +/- 7, mean BMI: 27.9 1.4 Kg/m2), whose obesity was not associated with impaired glucose tolerance (IGT), binge eating, nor endocrine diseases. Their daily HS profile (orexigram) was analysed chronobiometrically. The moderately hypocaloric diet with a substitutive meal reduced the daily HS by about 10% by the fourth week. This reduction was apparently due to a tonic and amplitude modulation of the HS CR and was not accompanied by its disruption. No conclusions, however, could be drawn with regard to its orectic and clinical effects beyond four weeks.