The defendant's right to a full defense may require the disclosure of the identity of informants who provided the information leading to the defendant's arrest. The guarantee of anonymity, however, is often a condition for the informant's help. Police must be aware of the extent to which an informant can be involved in a transaction without creating a substantial risk that the informant's identity will later have to be revealed. The defense of entrapment may be available to a defendant who contends he would not have committed the crime but for the enticements of undercover officers. Police must show that any reluctance the defendant may have had to commit the offense was based on the fear of getting caught. The exclusionary rule, which makes evidence obtained in violation of the defendant's constitutional rights inadmissible at trial, presents unique problems in drug cases. Also, drug defendants may claim discriminatory prosecution in attempting to show they were singled out as a target for police and prosecution efforts.