Alpinia speciosa Schum or A. nutans is a plant of the Zingiberaceae family, known popularly as "colony" (colônia) and used as a diuretic and to control hypertension. We have determined the concentration of Na+ and K+ found in the alcoholic extract and in the tea concoction. They contained 51.0 mEq Na+, and 132 mEq K+ in the extract, and 0.0 mEq of Na+ and 26 mEq K+ in the tea. Phytochemical analysis of the leaves demonstrated the presence of catecquic tanins, phenols and alkaloids, and also some essential oils. When injected intra-peritoneally the hydroalcoholic extract, in a dose range of 100 to 1400 mg/kg, (or 2500-18000 mg/kg orally) produced in mice: writhing, psychomotor excitation, hypokinesis and pruritus. The LD50 by ip was 0.760 +/- 0.126 g/kg and 10.0 +/- 2.5 g/kg by oral administration for the hydroalcoholic extract. Subacute toxicity made by injecting daily for 30 days the LD10 in rats caused an increase in transaminases and lactate dehydrogenase, whereas other parameters such as blood glucose, urea and creatinine were normal. A histopathological analysis of liver, spleen, gut, lung and heart showed no alterations. The drug also produced a prolongation of the sleeping time. The hydroalcoholic extract induced in the rat and in the dog a dose-dependent fall in blood pressure in doses of 10 to 30 mg/kg. In isolated atria the extract induced a reduction of the frequency and in the inotropic responses. Neither the extract nor the tea had an effect on the diuresis of the rat.