The effect of uterine distension on the cervix was studied in 16 women (mean age 38.4 years). Carbon dioxide was infused, in increments up to 50 ml, into a condom-ended catheter introduced into the uterus. The response of uterine and cervical pressures to uterine distension was determined before and after anesthetizing the uterine body and the cervix, respectively. Upon slow uterine distension, the cervical pressure increased (p < 0.01), while the uterine pressure showed insignificant changes (p > 0.05). Rapid distension led to cervical pressure decrease (p < 0.01) and increase of uterine pressure (p < 0.01). The cervical pressure did not respond to slow or rapid inflation of the anesthetized uterus, neither did the anesthetized cervix respond to uterine inflation. A reflex relationship seems to exist between the uterine body when distended and the cervix, which we call ‘uterocervical reflex’. The study demonstrates that the uterus behaves differently under physiologic and pathologic conditions. Upon slow uterine distension as in pregnancy, the uterus adapts by uterine dilatation and cervical tightening. In pathologic conditions which distend the uterus rapidly, the latter reacts with uterine contraction and cervical dilatation, discharging the uterine contents. Dysfunction of the uterocervical reflex may result in uterine and cervical disorders. The reflex may thus be included as a diagnostic tool in such disorders.