Myelomeningocele (MMC) is the most common cause of neurogenic-bladder-dysfunction (NBD). We recently developed a novel retinoic-acid (RA) induced MMC model in fetal rats. The objective of this study was to use this model to assess functional and structural characteristics of the detrusor muscle in MMC-associated NBD. Time-dated pregnant Sprague-Dawley rats were gavage fed 60mg/kg RA dissolved in olive oil or olive oil alone (E10). Bladder specimens from OIL (n=71), MMC (n=79), and RA-exposed-no-MMC (RA, n=62) were randomly assigned for functional, histopathological, and protein analysis. The expression patterns of -SMA, myosin, desmin, vimentin, and collagen III and I were analyzed. Spatial and temporal distribution of nerve fibers within the detrusor muscle was monitored by neurotubulin--III throughout gestation. Neither OIL, MMC, nor RA detrusor responded to field-stimulation. MMC bladders showed a significant decrease in contractility after KCl and bethanechol stimulation compared to OIL and RA bladders. Detrusor morphology and expression patterns of smooth muscle markers were similar between groups. OIL and RA bladders were densely innervated, possessing abundant intramural ganglia and nerve trunks. In MMC bladders, neurotubulin--III positive nerve fibers were markedly decreased with advancing gestational age and were almost completely absent at term. We conclude that the biomechanical properties of fetal rat MMC bladders are analogous to that seen in humans. Decreased nerve density indicates loss of peripheral neural innervation. The early observation of decreased innervation and decreased contractility in the absence of morphologic abnormalities in muscle structure supports a pathophysiologic hypothesis that denervation is the primary insult in MMC-associated NBD.