There are several reports on the weak contractile activity of uterus in the prolonged pregnancy. Some investigations showed that the weak contractile activity is associated with the low contents of RNA, proteins and glycogen in the myometrial cell. The material was obtained from caesarean sections in 27 patients with prolonged pregnancy and 30 patients with normal pregnancy. It was found a diminished contents of glycogen and lipids in the myometrial cell, and a decreased activity of phosphorylase and alkaline phosphatase but an increased activity of acid phosphatase. The lower content of energetic material and changes in the activity of the enzymes shows that the metabolism of the myometrial cell is impaired in prolonged pregnancy. One can suppose that the lowered level of estrogens is responsible for the described changes. The lower level of estrogens probably causes the decrease of 3'5' AMP in the myometrial cell with the impaired cell metabolism as a consequence. This may be one of the causes of a weak uterine contractile activity in the prolonged pregnancy.