During the third quarter of calendar year 1993, the DMP collected samples in 19 metropolitan areas. It purchases 172 exhibits, 166 of which contained heroin. The purity of these exhibits averaged 34.6 percent for all exhibits that contained heroin, with a low of 0.8 percent in Miami and a high of 97.8 percent in New York City. A total of 30 exhibits were of southeast Asian origin, with an average purity of 33.1 percent. Four exhibits were of southwest Asian origin, with an average purity of 33.1 percent; and four exhibits were of southwest Asian origin, with an average purity of 28.4 percent. Forty exhibits were of Mexican origin, with an average purity of 30.4 percent. Twenty- two exhibits were of South American origin, with an average purity of 59.3 percent. Sixty-eight exhibits were of unclassifiable origin, with an average purity of 30.2 percent. The average cost per milligram of pure heroin by source area is presented. Extensive tabular data