A new sequential test has been used to compare the effect of paracetamol and placebo on uterine cramping. Paracetamol was significantly superior to placebo at the 5% level. 75 patients were included in the trial, whereas in a fixed sample study 90 patients would have been required to obtain the same significance level and power. The magnitude of the difference in treatment effect was estimated following the sequential test. In addition to the effect on uterine pain, which was the primary variable, the effect on episiotomy pain was also estimated. Paracetamol was also superior to placebo against the episiotomy pain.