A significant positive correlation was found between the liquefaction time of human seminal coagula and bound sialic acid. There was also a similar relationship between bound sialic acid and the enzyme sialyl-transferase. This suggests that the degree of sialylation of the components of seminal coagulum are important in determining the liquefaction time of the coagulum. These results support previous findings. The coagulum is considered to be composed of glycoprotein-metal ion complexes, and the initial stage of liquefaction results from the reduction of these metal ions by L-ascorbic acid. The removal of hydrogen peroxide, generated by the oxidation of L-ascorbic acid, requires the presence of glutathione peroxidase and glutathione reductase. These enzymes have been identified in human seminal plasma and their possible physiological importance is discussed.