In the foetal membranes that ruptured spontaneously or by means of amniotomy during term vaginal deliveries the activity of tissue inhibitors of metalloproteinases was evaluated. Samples were taken from the proximity of the rupture line. Almost twofold lower TIMPs activity in the naturally ruptured membranes was observed. We conclude that during normally proceeding term vaginal delivery the activity of TIMPs in the lowermost pole of the amniotic sac is decreased, what may play very important role in the mechanism of the term rupture of the foetal membranes.