Smilax macrophylla Vers., administered per os at the doses of 1 or 2 g/kg in normal rats or in rats made hyperuricemic and hyperuricosuric by potassium oxonate (250 mg/Kg p.o.) or fructose (4 g/Kg p.o.) does not modify diuresis, but increases the excretion of uric acid and allantoin in normal rats and in those pretreated with fructose, whereas it is inactive in oxonate pretreated rats. Allantoinemia is not modified by fructose or oxonate, whereas uricemia is modified.