Independent groups of rats were compared drinking in response to either water deprivation or osmotic thirst induced by intraperitoneal injections of hypertonic saline. When water or a palatable saccharin solution served as the drinking fluid, deprivation and osmotic thirst produced comparable fluid intakes. In contrast, when a saccharin solution previously associated with the aversive effects of lithium served as the drinking fluid, animals injected with hypertonic saline drank substantially less than water deprived animals. Experiment 2 indicated that this hyperreactivity to a conditioned aversive flavor in animals suffering from osmotic thirst was due to the reduced palatability of the saccharin flavor rather than the previous experience with lithium. Experiment 3 showed that the effect also could not be attributed to differential taste-aversion learning, handling, food deprivation or weight loss before the test sessions. The phenomenon is discussed in terms of various differences between thirst induced by water deprivation and thirst induced by acute cellular dehydration.