Although rodents readily associate virtually any distinctive flavor with gastrointestinal illness when the flavor and illness have been paired, experience with a flavor can provide information that interferes with later attempts to produce aversions to the familiar taste. The vaginal secretion of female hamsters carries sexual information for males, which does not depend on previous experience, and that built-in information might also be expected to interfere with associations between the flavor of the secretion and illness. Surprisingly, male hamsters show dramatic changes in behavior toward the vaginal secretion when its presentation has been followed by lithium chloride poisoning, suggesting that mammalian responses to sex pheromones are far more easily modified by experience than has been supposed.