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Abstract: Ethnopharmacological relevance: Smilax canariensis is an endemic species of the Canary Islands, popularly known as “Zarzaparrilla sin espinas”. The rhizome, leaves and stem of this species has wide use in folk medicine practice on the islands, where they are habitually employed as diuretic. Aim of the study: In this paper we report on the diuretic activity in experimental animals of several fractions of the methanol extract of this species. Materials and methods: Four fractions of the methanol extract of the rhizomes, leaves and stem of Smilax canariensis (50 and 100mg/kg), Furosemide and Hydrochlorotiazide (10mg/kg), were orally administered to laboratory animals to evaluate their diuretic activity. Water excretion rate, pH, conductivity, and content of Na+, K+ and Cl− were measured in the urine of saline-loaded mice. Results: All the studied extracts showed an interesting increase of the diuresis, although the n-buthanol (27%; p <0.05) and ethyl acetate extract (35%; p <0.01), at 100mg/kg p.o., showed the most interesting diuretic activity, which suggested that this diuretic effect is associated with the compounds contained in the fractions of intermediate polarity (ethyl acetate and n-butanol), decreasing in the most extreme apolar and polar sub-extracts (dichloromethane and methanol: water respectively). The increase in diuresis produced by these two extracts was very close to the values of Hydrochlorothiazide (32%) or Furosemide (39%), used as reference diuretics. Conclusions: These data, together with previous results on the aqueous and methanol extracts, reaffirm assertions made regarding the effectiveness of the extracts of this plant against urinary pathologies in the Canary Islands folk medicine. [Copyright &y& Elsevier]