In order to demonstrate possible modifications of circadian rhythms of plasma proteins in elderly, we measured every four hours during 28 hours in 14 aged (greater than 60 years) subjects orosomucoid, alpha-1-antitrypsin (AAT) and ceruleoplasmin (Cp). A circadian rhythm of the 3 proteins was significantly detected: the 24 hour mean values of orosomucoid and AAT were higher in elderly compared to young subjects but not difference was detected concerning Cp. As far as acrophase and amplitude of these rhythms were concerned no statistical differences were found between elderly and young subjects.