Studies on PCP and violence are organized according to the types of subjects studied: PCP users in treatment (drug abuse or psychiatric), PCP users in the criminal justice system, or PCP users at large in the community. Within each of these three categories, this report describes the relevant studies and evaluates them. The evaluations emphasize methodological and measurement-related issues. Unanswered questions and directions for future research are identified. Overall, the study concludes that studies to date have not yielded enough evidence to determine whether PCP use increases violent crime. There are two reasons for this. First, the recent PCP-violence studies have too many serious methodological problems. These problems involve four areas necessary for making a valid causal inference: whether valid measurement of PCP use and violent crime was used, whether the amount of violence was related to the amount of PCP used, whether PCP use preceded violence, and whether confounded variables were ruled out. Second, in those studies in which there were fewer problems, such as the more recent studies of PCP users in the criminal justice system, contradictory findings were reported. These findings were limited because arrest data were used. The findings are still useful, however, in providing direction for future investigations. 3 tables, 15 notes, and 50 references