The distribution of adrenoblocking drug pyrroxan in the blood plasma and different organs of albino rats had been studied. A rapid appearance of pyrroxan in the brain liver, kidneys, and other organs was shown; its selective accumulation in the hypothalamus was found. As revealed spectrofluorimetrically unchanged pyrroxan molecules disappeared from the plasma and the organs within 2 hours. When pyrroxan-14C was used the radioactivity in the organs was demonstrated for 24 hours, and in the plasma for several days; this indicated the formation of pyrroxan metabolites or its complexes with the plasma proteins and structural elements of the organs. The selective accumulation of pyrroxan in the hypothalamus can account for the high efficacy of this drug in different hypothalamic disorders coursing with the overexcitation of the sympathetic nervous system.