RESUMEN
<p><b>OBJECTIVE</b>To explore the expressions of endothelial nitric oxide synthase (eNOS) and cytochrome P450 (aromatase) in the testis of sexually mature male SD rats and their significance.</p><p><b>METHODS</b>Eighteen male SD rats, 6 five-week, 6 seven-week and 6 ten-week old, were selected for this study. Paraffin sections of the left testis were made and the expressions of eNOS and P450 observed by the immunohistochemical ABC method.</p><p><b>RESULTS</b>Positive expressions of eNOS and P450 were found to be + + +, + and + + in the Leydig cells of the five-week, seven-week and ten-week old rats, respectively, and they were also observed in a few spermatocytes, though with no regularity.</p><p><b>CONCLUSION</b>In the Leydig cells of sexually mature male SD rats, eNOS and P450 are differently expressed in different stages of sexual maturation, and they are correlated as well.</p>