This paper deals with the specific identification of several thiazide, potassium-sparing and loop diuretics. The liquid chromatographic behaviour of these compounds is studied. Different organic modifiers (methanol, acetonitrile and tetrahydrofuran) are compared in terms of selectivity for the thiazide diuretics. An acetonitrile-water (40:60) eluent can be used to identify the thiazide diuretics. The loop and potassium-sparing diuretics are well chromatographed at an acidic pH in the presence of propylamine hydrochloride. This study enables us to select the right mobile phase composition for any given selectivity or resolution. The determination of the dead volume in different chromatographic systems is also discussed. A mixture of organic solvent and deuterium oxide in the same volume ratio as the eluent is used as dead volume marker. The signal is monitored with a UV detector at low wavelength.