RESUMEN
Mikania glomerata (guaco) is a plant well known in Brazil for its therapeutic properties, especially in the treatament of respiratory diseases. Coumarin and flavonoids are active compounds of M. glomerata leaves and have been reported to cause adverse effects on the organism, including antifertility activity in famale rat and male dog respectively. This work analyzes the effect of short-term administration of M.glomerata hydroalcoholic extract on vital organs, of the reproductive system and sperm concentration of mature male wistar rats. Treated animals received 1 ml of the extract at a dose of 1.1 g/kg of body weight for live days. Body and organs weights, sperm production and food consumption were evaluated. No body weigth reduction and no toxic effect on the organs, gamete production or food intake were detected in any of the groups analyzed, given the experimental protocol used.