The following trends were observed between 1999 and earlier years. In 1999, there were an estimated 554,932 drug-related ED episodes and 1,015,206 ED drug mentions in the United States. Nationally, the number of ED episodes and mentions remained relatively stable from 1998 to 1999. The four drugs mentioned most frequently in ED reports were alcohol-in-combination, cocaine, marijuana/hashish, and heroin/morphine and were statistically unchanged from 1998 to 1999. In 1999, marijuana/hashish mentions exceeded heroin/morphine mentions, changing a rank ordering of illicit drug mentions that had been constant since 1990. From 1998 to 1999, total drug-related ED episodes were stable for gender, race/ethnicity, and most age subgroups. For patients age 12 to 17, total drug-related episodes decreased 11 percent from 1998 to 1999. For the same age group, mentions of cocaine, heroin/morphine, marijuana/hashish, and methamphetamine/speed were statistically unchanged from 1998 to 1999. In drug-related ED episodes in 1999, dependence and suicide were the most frequently cited motives for taking the substances. Between 1998 to 1999, drug-related ED episodes involving suicide decreased 8 percent. Among the 21 metropolitan areas oversampled in DAWN, 3 had significant increases in drug-related ED episodes from 1998 to 1999: Los Angeles, Denver, and Phoenix. ED mentions of PCP/PCP combinations did not change significantly from 1998 to 1999. No significant changes occurred in LSD mentions from 1998 to 1999. 15 figures, 4 appendices, and 56 tables.