In the Colombian traditional medicine, an infusion made of the entire plant Salvia scutellarioides (known locally as mastranto or oreja de perro (dog's ear)) is used for its antihypertensive and diuretic effects. However, experimental studies have never been done to validate the reported effects.In the current study, a rat model was used to determine the effect of S. scutellarioides on rat diuresis and urinary electrolytes concentration.Twenty-four male Sprague-Dawley rats were distributed in four groups: Group 1--normal saline solution, Group 2--furosemide (10 mg/kg), Groups 3 and 4 with S. scutellarioides infusion, 1 g/kg and 2 g/kg respectively. All treatments were administered in a volume of 25 ml/kg of rat weight. After treatment, the rats were placed in a metabolic cage for 6 hours. During this period, urinary excretion was monitored and quantified. At the end of 6 hours, the urinary electrolyte concentrations were measured.The administration of S. scutellarioides at doses of 1 and 2 g/kg produced a significant increase in diuresis when compared to the control group (p < 0.01). The administration of S. scutellarioides at these doses also increased the urinary excretion of potassium and chloride.These results corroborate the apparent diuretic activity of S. scutellarioides described by traditional herbalists and possibly explains its reported antihypertensive effect. Further studies are required to determine the pharmacological and toxicological profile of the plant.