decoction, while the others received 1 mL of water instead for 2 weeks. Urine samples (24 h) were collected individually at 1, 3, 7, and 14 days for physicochemical analysis. On completing the treatment the kidneys were collected and analysed by light microscopy. RESULTSThe water intake and diuresis decreased in the treated rats; there was no significant difference in urinary pH between the groups. Urinary chemistry was apparently unaffected by the plant extract, except for the magnesium content, which was higher in treated rats. Crystalluria was characterized by the excretion of large CaOx monohydrate and dihydrate crystals in untreated, but smaller crystals in treated rats. The histology showed large deposits of CaOx crystals in all parts of the kidney in untreated rats but with almost no deposits in those of treated rats. CONCLUSIONH. hirsuta has an impressive prophylactic effect on CaOx stones in nephrolithic rats; the effect did not seem to be mediated by biochemical or diuretic changes.