About 100 male SD rats aged 2, 5, 10, 18 and 24 months (each age group for about 20 rats) were used in the anti-senility experiment. The animals of each age group were further subdivided into two groups randomly: one group administered with Wuzi Yanzong Liquid (WYL) daily for 5 weeks, and the other group with normal saline. After treatment, plasma testosterone (T) and estradiol (E2), hypothalamus norepinephrine (NE), dopamine (DA) and serotonin (5-HT) levels were determined. In comparison with younger groups, the 18 and 24 months old rats administered with saline had markedly lowered plasma T, hypothalamus NE and DA levels, and elevated 5-HT, E2 levels and 5-HT/DA, E2/T ratios; while in the 18 and 24 months rats administered with WYL the above mentioned changes were much less remarkable. Since WYL only raised plasma T level in old rats but not in younger ones, this drug seems to have different action from testosterone preparations. In another animal experiment, the reproduction promoting effect of WYL was shown by the increase of sperm count and motility of sperms in old male rats as well as its reproductive ability.