The data presented are based on undercover heroin purchases made by DEA (Drug Enforcement Administration) agents on the streets of these cities. This Domestic Monitor Program (DMP) collected samples in Atlanta, Baltimore, Boston, Chicago, Dallas, Denver, Detroit, El Paso, Houston, Los Angeles, Miami, Newark, New Orleans, New York, Orlando, Philadelphia, Phoenix, San Diego, San Francisco, San Juan, Seattle, St. Louis, and Washington, DC. In 1999, both the average retail purity and average price per milligram of pure heroin declined from 1998 levels. At 35.7 percent, the average purity decreased six percentage points from a 1998 high of 41.6 percent. South American heroin samples continued to have the highest purity and Mexican samples the lowest. In 2000, heroin average price and purity changed slightly from 1999 levels. The 2000 average price of $1.07 increased from the average price of $0.87 in 1999. At 36.8 percent, the 2000 average purity increased slightly from 35.7 percent in 1999. Overall, South American heroin samples had the highest average purity, 48 percent, with an average price of $0.76. Mexican heroin samples continued to be the most expensive, with an average price of $1.60, but they had the lowest average purity at 20.8 percent, a decrease of eight percentage points from 1999. Data on purity and price are reported for each of the 23 cities for each year. 13 tables and appended definitions