& To evaluate the effect of chymotrypsin on the examination of alpha-glucosidase activity in seminal plasma, thirty-nine samples of fresh liquefied semen with or without chymotrypsin and forty-eight samples of fresh un-liquefied semen with chymotrypsin were determined for the total alpha-glucosidase activity in seminal plasma. The total alpha-glucosidase level of each sample was assayed by the method of glucose oxidase. The correlations between alpha-glucosidase level and semen parameters, including semen volume, pH, sperm concentration, grade a and b motility and total motility, were analyzed with SPSS 11.0 software. The results showed that chymotrypsin had no effect on seminal alpha-glucosidase activity determination. Chymotrypsin could improve the liquefaction for un-liquefied semen, and there was no significant difference of alpha-glucosidase activity between liquefied and un-liquefied semen samples. There were significantly positive correlations between seminal alpha-glucosidase activity (U=ml) and sperm concentration (r ¼ 0.338, p ¼ 0.015) and between total alpha-glucosidase activity (U=ejaculate) and semen volume (r ¼ 0.677, p ¼ 0.000). However, there was no significant correlation between alpha-glucosidase level (U=ml) and semen volume, pH, sperm motility or grade a and b motility (r ¼ À0.234 $ 0.077, p ¼ 0.099 $ 0.993). The data indicated that chymotrypsin could be added into the Address correspondence to Dr. Jin-Chun Lu, Department of Reproduction and Genetics, Nanjing General Hospital, PLA, 305 East Zhongshan Road, Nanjing 210002, P. R. China. E-mail: jclu@jlonline. un-liquefied semen samples for alpha-glucosidase activity determination, and there were different correlations between seminal alpha-glucosidase level and various semen parameters.