The deep body temperature of the unrestrained laying hen was measured continuously by the telemetry system with the simultaneous recording of the time of oviposition. The photoregimen was 14L:10D. The body temperature increased during either the natural oviposition or the oviposition induced by LH. Premature ovipositions were induced by the intravenous injection of vasopression or prostaglandin F2α after the induction of ovulation by LH. The peak time of body temperature was not advanced by the prematurely induced oviposition. A small rise in body temperature was observed 6.2 hr after the injection of LH. This can be considered due to the occurrence of ovulation. One of the causes of a rise in body temperature at oviposition may be secretion of prostaglandin.