It is disclosed a method for determining the biological activity of defibrotide, which comprises the steps of: a) bringing into contact defibrotide, mammalian euglobulin and a substrate specific for the plasmin which, by reaction with the plasmin, provides a measurable product； and b) measuring the amount of product formed at successive times, to thereby determine the biological activity of the defibrotide. Liquid defibrotide formulations are also disclosed, preferably water solutions, having a defined biological activity and, in particular, having an activity of 25 to 35 IU/mg of defibrotide, preferably from 27.5 to 32.5 IU/mg and, more preferably, from 28 to 32 IU/mg.
