In 1961 the U.S. Supreme Court in Mapp v. Ohio reversed its decision in Wolf v. Colorado which left it to the States to develop methods for deterring unreasonable police conduct. "Mapp" ruled, on the other hand, that evidence obtained in violation of the fourth amendment is inadmissible in State criminal prosecutions. The Court concluded that the experience of the States with alternative remedies for police misconduct had proven futile and ineffective. Essentially the Court found that other than the exclusionary rule, no other method had been effective in deterring police violations of the Constitution. Since "Mapp," a number of U.S. Supreme Court decisions have significantly diminished the scope and applicability of the exclusionary rule. In United States v. Calandra (1974), the Court concluded that application of the rule to a particular proceeding depended on use of a balancing-of-interests approach that would weigh the deterrent effect of the rule in a particular situation against the cost of being unable to use probative evidence. In United States v. Leon (1984), the court held that evidence obtained by police who had acted in the belief that a search warrant was valid could not be suppressed, even though the search warrant was subsequently found invalid. This "good faith" exception should be the last abridgement of the exclusionary rule if we are to avoid the annihilation of the single doctrine that prevents the police from benefiting from unlawful evidence collection. 22-item bibliography