The area most widely associated with osmoreception has been the lateral preoptic nucleus. However, Hatton (1976) proposed that the nucleus circularis could be the actual osmoreceptor in the hypothalamus. The present study supported Hatton by using 30 rats which were randomly assigned to sham, lateral preoptic, and nucleus circularis lesion groups. After a 2-week post-operative period, half of each group was injected with isotonic saline while the other half was injected with hypertonic saline. Water consumption was measured at 10-minute intervals for one hour. Following a 4-day recovery period, the injection procedure was reversed. Analysis of difference scores, computed by subtracting the amount of water consumed after isotonic injection from the amount of water consumed after hypertonic injection, revealed a significant difference between the nucleus circularis group and the other two groups.