Nerve growth factor (NGF) affects morphology and function of isolated and cultured seminiferous tubules from human testis. Quantitative determination of this neurotrophic protein revealed an amount of 5.4 ng per g human testis, suggesting a crucial function of NGF in spermatogenic tissue. With the use of immunohistochemical methods target cells for NGF were identified within the lamina propria. NGF receptors were also visualized on sympathetic nerve fibers crossing the interstitial compartment among adjacent tubules and spatially correlated blood vessels. NGF receptors could be demonstrated on isolated lamina-propria cells even after 2 weeks of culture. Most of the NGF receptor-bearing cells differed from myoid cells of the lamina propria expressing desmin, a marker for smooth muscle. However, some NGF receptor-expressing cells were found sharing morphological and structural similarities with myoid cells. The present data indicate the existence of a NGF-responsive lamina-propria cell that influences the tubular wall and also the seminiferous epithelium.