Fenquizone is the diuretic drug. The distribution of fenquizone labelled with 14C in mice was studied by means of an autoradiographic technique. High concentration of radioactivity was found in the intestine, liver, kidney, blood, myocardium and skeletal muscles in decreasing order at various times after oral administration. The labelled compound did not cross the blood-brain barrier. Fenquizone is a saluretic with a quinazolone structure which acts by blocking reabsorption of sodium in the proximal tubule and the ascending branch of the loop of Henle, as well as in the proximal section of the convoluted distal tubule. At low doses fenquizone has an hypotensive action without showing the characteristics secondary effects of diuretics so that it can be employed for long-term treatments without any risk. Fenquizone showed also a significant decrease of symptoms (headache, dizziness) due to hypertension. No undesirable side effects were observed.