The negative side effects of aversive control have been extensively discussed in clinical literature and textbooks. The symmetry between aversive and appetitive control in basic experimental research implies that parallel negative side effects of reward exist. These negative side effects are described and their implications for clinical practice and research are discussed.DESCRIPTORS: reinforcement, punishment, iatrogenic illness, symptom substitution, generalization A behavioral psychologist, Dr. B, once had a student, N, who was quiet and withdrawn. He decided to try to encourage N to participate in research discussions. He consulted all of the latest behavior therapy textbooks and designed an intervention program. Each time N spoke of research, Dr. B said enthusiastically how nice it was to hear N's opinion and what good points N was making (all of which were true). Soon N's rate of verbal behavior had increased enormously. Unfortunately, N also began talking about topics other than research. In fact, N's major topics of discussion were about the relative merits of different kinds of dog food and which city had the best mass transportation system. N spent several hours each day seeking out Dr. B at the office, the lab, and on the phone. N spent so much time looking for and talking to Dr. B that N's interaction with other students was virtually eliminated. Dr. B's life became miserable. This time Dr. B consulted a clinically oriented colleague who suggested that he punish N for all of the excessive verbal behavior. Dr. B, of course, abhorred the use of this method forThe order of authorship was determined by a random process. We thank