In an attempt to elucidate the function of early human trophoblast and to find to find an enzymatic difference in normal pregnancy and abnormal pregnancy of hydatidiform moles, activities of lactic dehydrogenase (LDH) and alkaline phosphatase (AP) in the maternal serum and the fluid of hydatidiform moles were measured, and comparisons were made with those of normal non-pregnant and pregnant women. 1) Both of the the enzyme activitied in the maternal sera of hydatidiform moles showed slighly higher than pregnant, yet close to non-pregnant levels, which suggests that enzymatic patterns in hydatidiform moles are more similar to those in non-pregnancy than in pregnancy. 2) Very high activities of both enzymes were demonstrated in the mole fluid. However, ther existed a great variation in their enzyme contents among different moles. Thus, LDH in the mole fluid showed from 3 to 300-fold higher, and AP 2 to 30-fold higher activities than those of the maternal sera. It was suggested that this variation in the enzyme conterts of mole fluid might reflect a possible existence of quantitative difference among different moles in glycolytic metabolism of early trophoblast. 3) During the entire period of pregnancy, both LDH and AP serum levels were lower than those in non-pregnancy. Howerver, upon delivery and until 48 hours after delivery these lowered enzyme levels were increasesd near to and/or above normal non-pregnant levels with a greater magnitude of the increase in AP activities.