Abstract. The hyperthermic effect of purified lipopolysaccharides (Pyrexal, Wander) was tested and analyzed in pregnant rabbits. The fever produced premature deliveries-probably caused by oxytocin, released from the posterior pituitary-in 50% of 40 tested rabbits on the 31st day of gestation. Injections of Syntocinon had a roughly equally strong effect. In control animals injection of saline did not accelerate delivery.

The offspring of several animals, in which hyperthermia had been induced, were born dead.

Fever during pregnancy thus can result in premature delivery and in injury to the fetus. Fever and febrile conditions occurring during pregnancy should therefore be treated as promptly and as effectively as possible.