The article presents a survey of preterm rupture of the amniotic membranes at term (more than 1 hour prior to uterine contractions) and preterm (< 37 weeks). The diagnosis of rupture can be suspected from the history alone in 90% of the cases, and confirmed by inspection. In doubtful cases the pH in fluid from the posterior fornix of the vagina is determined and microscopy is performed. Amniotic fluid is alkaline. Microscopy of a dried specimen shows "ferning" when amniotic fluid is present (crystallization test). Staining with Nil blue will reveal orange foetal cells in fresh specimens, usually only late in pregnancy (after the 38 week). The crystallization test is useful, however, in all three trimesters. The cause of membrane rupture and of chorioamnionitis may be infection. Chorioamnionitis is a serious clinical condition, but can be subclinical and may occur with intact membranes. It can lead to preterm delivery. It is important that chorioamnionitis be diagnosed (maternal fever, tachycardia, uterine contractions, abdominal pain, foul smelling vaginal discharge and elevated C-reactive protein). The condition is treated with antibiotics and labour must be induced.