Frequency curves were constructed for intensity, frequency and duration of uterine contractions during normal active phase labor in 20 parturients. This method of analysis emphasizes the variability in uterine contractions during normal labor. The uterus is a smooth muscle, and frequency-curve analysis demonstrates its irregular rhythmicity. Normal cervical dilatation rates during labor are not related to either rhythmical or n on rhythmical uterine action. Discussions and teachings concerning myometrial activity should be framed in terms of its smooth muscle character rather than any resemblance to myocardial activity.