目的：探讨新生儿昼夜排尿特性、膀胱容量及血浆、尿液渗透压变化。方法：42例新生儿(男22例，女20例)，根据日龄分为A，B，C 3组，3组日龄分别为～3 d，～7 d，>7d。记录昼夜排尿时间、尿量，以膀胱B超机测量膀胱残余尿量，以FM-6型全自动冰点渗透压仪测量血浆、尿液渗透压。结果：①A组昼夜尿量，排尿次数与B，C组比较，差异有显著性意义(P<0.05)。②A，B，C 3组膀胱排空率(ER)，膀胱最大容量(MBC)及血浆、尿液渗透压分别为(0.80±0.07)，(0.82±0.09)，(0.79±0.10)；(56±6)，(65±14)，(61±15) ml；(285±5)，(287±7)，(286±8) mOsm/L；(202±59)，(185±65)，(216±92) mOsm/L；统计学上无显著性差异(P>0.05)。③以逐步回归分析法建立估测膀胱最大容量的最优回归方程，膀胱最大容量=42±0.17X(ml)，X为10 AM～6 PM尿量，F=15.561(P<0.01)。结论：正常新生儿膀胱稳定，几乎完全排空。新生儿肾脏浓缩功能无昼夜差异。

OBJECTIVE: To assess micturition characteristics, bladder capacity and plasma and urine osmolarity in neonates. METHODS: Fortyfive neonates were divided into three groups according to post natal ages (Group A=～3 d, Group B=～7 d, Group C=>7 d). The time of micturition and voided volume were recorded. The residual urine volume was detected using a bladder volume instrument (BladderScan BVI 2500). Plasma and urine osmolarity were measured using the FM-6 pattern freezing point osmometer. RESULTS: ① There were significant differences (P<0.05) in the daynight voided volume and voided frequency between Group A and Groups B and C. ② The bladder emptying rates, maxium bladder capacity(MBC) and plasma urine osmolarity of Groups A, B and C were 0.80±0.07, 0.82±0.09, 0.79±0.10; 56±6, 65±14, 61±15 (ml); 285±5, 287±7, 286±8 (mOsm/L); 202±59, 185±65, 216±92 (mOsm/L) respectively and there was no significant difference between the 3 groups. ③ The multiple stepwise regression method was used to estabilish the best regression equation for predicting the MBC, which was 42±0.17X (ml) ［X=8 hours (10 Am～6 Pm) voided volume, F=15.561 (P<0.01)］. CONCLUSIONS: The bladder of normal neonates empties almost completely and its function is stable. There is no difference in the renal concentration function of neonates between day and night.