&NA;Two thousand seven hundred ninety two contraction stress tests (CST) were analysed. Oxytocin was administered in 1730 of these to stimulate uterine contractions and the hyperstimulation which occurred in 48 tests (2.8%) was studied extensively. Seven patients went into labor within 24 hours of the hyperstimulation. Two infants weighed less than 2500 g. One was mature but small‐for‐dates and the other (who died neonatally) had a trisomy‐18 syndrome with severe congenital abnormalities. There were no other intrapartum or neonatal complications. Ten CSTs demonstrated hypertonicity without any preceding oxytocin administration. No harmful effects from the hyperstimulation could be found.