We studied the effect of prenatal exposure to alcohol on later circadian rhythm in the rat. In the normal light-dark cycle, an 8-h phase advance brought forward the deep body temperature rhythm in control rats, although it had a smaller effect in prenatally ethanol-exposed rats. In long constant darkness, the phase response of the deep body temperature rhythm to a light pulse at the early subjective night was less marked in ethanol-exposed rats in comparison to controls. These results indicate that prenatal exposure to alcohol has a long-lasting effect on the light responsiveness of the deep body temperature circadian rhythm.