It is a new anti-hypertensive drug. Its pharmacodynamic profile shows a diuretic efficacy similar for a part of its activity to that of furosemide and a duration of action comparable with that of hydrochlorothiazide [l]. It has a mechanism of action that is relevant of a new concept of ionic transfer [24]. Current methods for assay of the drug from biological fluids are either scintillation counting with the 35S-labelled molecule or a densitofluorimetric method [W. In order to support pharmacokinetic studies, we have developed a selective reversed-phase high-performance liquid chromatographic (HPLC) method with UV detection of xipamide in plasma and urine samples. Its advantage is a rapid and easy extraction before a rapid separation.