T he changes in the mechanical behavior of cervical tissue observed at the end of gestation are in fact due to histological and biochemical changes. The inner circumference of the cervix in the nongravid state, having a well-ordered collagenous network, cannot reach the inner circumference value necessary to accommodate the fetal head. Therefore, the rearrangement of the collagen fibers into a more disorganized, looser network during pregnancy seems to be an important process in cervical ripening. In support of this idea are the numerous histological studies showing disorganization of collagen fibers at term in animals1,2 and women. 3,4 Biochemical changes of the cervical connective tissue ground substance components (eg, proteoglycans, glycoproteins, water content) are likely to play a major role in the disorganization of the collagen network. 5~6 In the human cervix the fibroelasticity seems to dominate, since the test results observed by several authors’.8 with the uterine cervix closely resemble the results for fibroelastic materials. In obstetrics, it is of great interest to quantitatively determine mechanical characteristics of the uterine cervix, particularly the ease with which the cervix can be dilated, in order to describe and understand the mechanism of human cervical dilatation. Digital internal pelvic examination is a fast and simple technique to study physical characteristics of the uterine cervix, and a number of clinical systems of quantifying cervical ripeness have been devised, most notable that of Bishop.g With these systems, a low score indicates an unripe cervix, and a high score, a ripe cervix. Unfortunately, these methods are subjective, and amalgamate several parameters, eg, that cervical consistency is presumably related to biochemical connective tissue changes whereas the other elements of the pelvic score (dilation, effacement, position, level of the presentation) are most likely related to myometrial activity. This is why several instruments were designed to quantitate the mechanical properties of the uterine cervix related to connective tissue changes (measurement of cervical compliance and cervical consistency),7,810 but the clinical application of such methods is very difficult and/or not accurate enough. We have developed a cervicotonometer to measure a distensibility index in the clinical practice that is based on the values of the force used to open the cervix and the inner diameter of the cervix obtained with each force used. The use of this instrument and results obtained with it will be described in this article.