A pharmacokinetic study of 3H-labelled 7-rhamnoglycoside of 5,7,3'-trihydroxy-4'-methoxyflavone (3H-diosmine) administered both i.v. and orally, shows the great ease with which it is absorbed in digestion. A very sharp difference in elimination between the two modes of treatment must be associated with a difference in metabolism. A study of fixation confirms this conclusion. In particular the fixation on the tunica vascularis, perhaps due to a metabolite, appears relatively late. Furthermore the existence of an enterohepatic cycle assures a permanent hepatic binding.