In this work we studied in rat the diuretic activity of Opuntia ficus indica (L.) Mill. (Cactaceae) waste matter. The cladodes, flowers and non commerciable fruits were collected in S. Cono (CT, Sicily) cultivation. Acute and chronic diuretic activity of 15% infusion of cladodes, flowers and fruits were assayed. Natriuresis, kaliuresis and the activity on fructose-induced hyperuricemia was also studied. The results show that O. ficus indica cladode, fruit and flower infusions significantly increase diuresis. This effect is more marked with the fruit infusion and it is particularly significant during the chronic treatment. The fruit infusion shows also antiuric effect. In all experiments cladode, flower and fruit infusions showed a modest but not significant increase in natriuresis and kaliuresis.