Much is known about discriminative stimuli established under either reinforcing or aversive stimuli and about how they work as conditioned reinforcers or conditioned aversive stimuli. However, little is known experimentally about discriminative stimuli established with both reinforcing as well as aversive events. It has been reported that the interaction between reinforcing and aversive events makes the discriminative function somewhat different from other discriminative stimuli (see Hearst & Sidman, 1961). Karen Pryor (2002) called this phenomenon the Poisoned Cue. She suggested that a cue, or SD, that is established using both reinforcing and aversive events leads to the breakdown of the behavior both preceding and following the cue. This may be due to an increase in avoidance behaviors and the uncertainty that exists regarding the consequence that will follow. The Poisoned Cue phenomenon is important because it reflects the majority of teaching situations in the real world. SDs in the real world are rarely taught with purely positive reinforcement or purely aversive consequences. This presentation will show an experimental analysis of the Poisoned Cue, and techniques to identify situations that might involve Poisoned Cues. It will also discuss ways to overcome these cues.