groups of clean KM mice were exposed to light for short, middle, long period respectively. After 10 weeks ,the content of testosterone of male and progesterone of female in serum were determined by RIA in each group. The results showed the content of testosterone in serum of male in long-period group was highter than that in the other two groups (P< 0.05); and that the content of progesterone in serum of female in the short-period group was lower compared with the long period group (P< 0.05).