A study was conducted of phencyclidine use by a national sample of 2,750 youthful drug abuse clients representing 97 drug abuse treatment programs. Data from this 1976-1977 client survey indicated that phencyclidine use is widespread. More than 31% of the subjects reported current or past use of phencyclidine, with males and females having similar exposure rates. While the sample cannot be viewed as representative, the data do indicate that phencyclidine is in use in all regions of the country with the highest rates reported in the Great Lakes and Midwest regions. Further examination of the data suggests that phencyclidine subjects tend to be multiple substance users who, on the average, take twice as many different substances as other youthful drug users. It was also found that more than half the phencyclidine subjects reported themselves as using the drug one or more times weekly over the course of a three-month period. Phencyclidine users were more likely than nonusers to report themselves as having had difficulties involving toxic reactions, self-destructive acts, and prior treatment episodes. (Author)