A total of 38 infants and children with myelodysplasia was selected for statistical comparison of the effects of medium-fill and slow-fill saline cystometry on detrusor pressure. Medium-fill cystometry was performed at 20% of estimated bladder capacity per minute (up to 25 cc per minute) and slow-fill cystometry at 2% (up to 2.5 cc per minute). In 26 cases the filling rate did not determine the change in detrusor filling pressure while in 12 the change in detrusor filling pressure was greater than 15 cm. water during medium-fill but not slow-fill cystometry (p = 0.001). In 24 cases the filling rate did not determine the occurrence of maximal detrusor pressure greater than 40 cm. water but in 14 such pressure was noted during medium-fill but not slow-fill cystometry (p = 0.0005). Excluding 10 children with coexisting vesicoureteral reflux, differences in the change of detrusor filling pressure greater than 15 cm. water and maximal detrusor pressure greater than 40 cm. water remained statistically significant (p = 0.01 and p = 0.005, respectively). It is concluded that detrusor pressure can be manipulated by varying bladder filling with saline solution.