For the better understanding of etiology of nocturnal enuresis, the development of bladder function with children's age should be taken into consideration. Functional bladder capacity (FBC) and average urinary flow rate (AFR) are easy to measure and can be valuable indices for checking the bladder function of normal children. FBC is estimated by the volume of urine passed at the time of urgent desire to void, and AFR is defined as the quotient between voided volume and flow time measured with a

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... stop-watch. Using this method, FBC and AFR after water loading were measured in 102 nursery and school children, aged from 4 to 14 years. The data obtained were analysed using the techniques of variance analysis. The results are as follows; 1. FBC increases with age from 4 to 14 years. 2. FBC of boys is slightly, but definitely larger than that of girls. 3. AFR is approximately in proportion to square root of voiding volume. 4. AFR increases with age. There is a considerable correlation between AFR and FBC, which increases with age. However, AFR is not related to FBC alone. An age-dependent definite increase of AFR could be shown clearly by covariance analysis of the data. 5. AFR of girls is larger than that of boys.