ABSTRACT
<p><b>OBJECTIVE</b>To investigate the expression and the role of nitric oxide synthase (NOS) in the testis and epididymis of macaca fascicularis.</p><p><b>METHODS</b>The immunohistochemical ABC method was used to observe the localization of nitric oxide synthase in the testis and epididymis of the macaca fascicularis.</p><p><b>RESULTS</b>(1) nNOS immunoreactivity was found in the spermatogenic cells of seminiferous tubules, the epithelia of epididymal efferent ducts, sperm and the endothelia of blood vessels; (2) iNOS was expressed in the epididymal efferent duct, the sperm inside the duct, and the myoid cells and endothelia of blood vessels; (3) eNOS immunoreactivity was detected in the interstitial cells of the testis, the epididymal efferent duct, the sperm inside the duct, and the myoid cells and endothelia of blood vessels.</p><p><b>CONCLUSION</b>NOS is extensively expressed in the testis and epididymis of the macaca fascicularis and it may play an important role in such processes as spermatogenesis, sperm maturation and testosterone secretion.</p>