Through ethnobotanical surveys in Guatemala, about 250 plants were identified for use in the treatment of urinary ailments. From 67 of these, aqueous extracts were prepared to investigate their oral diuretic activity in albino rats after a dose equivalent to 1 g/kg of dried plant material. The trials demonstrated that in 33 cases urinary excretion was not significantly increased (less than 90%), in 20 cases intermediate activity was seen (90-189%) and in 14 cases high diuretic activity was noted (greater than 189%). Control treatment increased urine output an average of 36% while 25 mg/kg hydrochlorothiazide treatment increased urine output by 286%. In a select group of the most used local plants, ethanol extracts were tested for their effect on urinary excretion of uric acid and electrolytes. Of these, three plants significantly increased uric acid excretion as did the reference drug, probenecid, 25 mg/kg.