The effects of variation in fluid intake, of hard or softened drinking water, and of dietary calcium restriction on urinary relative saturation with calcium phosphates and magnesium ammonium phosphate were studied in 36 patients with neruogenic bladder. The relationship between urine volume and brushite saturation was statistically significant in 25 patients. For 8, an output of at least 4 liters per day should provide effective antistone therapy. For 17, an impossibly large volume (up to 11 liters daily) would be required. In two patients brushite saturation was significantly reduced in response to substitution of softened water for hard drinking, and in another two soft water combined with dietary calcium restriction had a similar effect. Unless urinary pH can be controlled, limitation of calcium intake is of no value in the majority of patients with neurogenic bladder and calculous disease.