Shao-Fu-Zhu-Yu-Tang (SFZYT) is reportedly beneficial to sperm. In this study, we examined sperm acrosomal activity and serum free radical changes to evaluate the possible mechanism of SFZYT. A clinical study evaluated the sperm count and motility in 36 patients with chronic prostatitis before and after treatment for 60 days. The results revealed a significant increase in sperm motility after treatment as evaluated by computer-assisted semen analysis (17.27 +/- 9.00 versus 28.29 +/- 10.00, p < 0.01). An increase in sperm quantity and quality was observed by count and morphology with a high-powered intravital microscope. To gain an understanding of the mechanisms that caused this effect, we assessed sperm acrosin activity levels before (10.6 micro lu/10(6)) and after medication (28.6 micro lu/10(6)) (p < 0.01). The levels of the free radicals was relatively higher before medication, 2144, compared to a normal value of 780 after medication (p < 0.01). In conclusion, SFZYT increased the motility and quality of human semen and this increase is related to an increase in sperm acrosin activity. SFZYT also works as a sperm antioxidant and antiaging agent.