In 3 lots of 15 rats, urinary proteins excretion (U.P.E.) during 6 hours periods is compared : 1) daily and nightly in physiological conditions, where U.P.E. increases nightly (+ 97,47%) : 2) daily, before and after theophylline injection, where U.P.E. increases after theophylline injection (+ 78,62%) ; 3) nightly, before and after theophylline injection, where U.P.E. increase is only tiny (+ 3,53%) after theophylline injection. So, in nightly physiological and in daily experimental conditions the important U.P.E. increases can be in part explained by those of renal functions. This result can explain after nightly theophylline injection (where renal functions are already very higher than in daily period) the so small nightly proteinuria increase with the xanthic diuretic ; it cannot be compared to the daily value, because the renal functions cannot increase beyond some limits. Lastly, the present paper exhibits how a pharmacomolecule (as theophylline here) can act differently daily and nightly and open a new investigation field in chronopharmacology of diuretics.