A personal method has been used to study spontaneous kinetic activity of the uterus in 50 women during puerperium following miscarriage between the VIIIth and XIIth weeks. Modifications induced were evaluated in several sessions (510 recordings) and at various periods of time, following administration of: 50 mg of 17B oestradiol, 200 mg natural progesterone, 500 mg of natural progesterone, 250 mg of 17 hydroxyprogesterone caproate and 500 mg of 17 hydroxyprogesterone caproate. In the case of some of the patients, hysterotonometry was evaluated following intravenous oxytocin loading. The results pointed to an activation of the uterine pacemaker after oestrogenic loading, and a clear-cut progestinic block of contractile activity.