Data were obtained from the University of Michigan's Monitoring the Future study, which uses a multi-stage sampling procedure to develop nationally representative samples of 8th, 10th, and 12th graders from the 48 continuous States. To increase the numbers of cases for analysis, the study combined data from 1996 to 2000. A total of 40,416 8th-grade girls, 37,977 8th-grade boys, 35,451 10th-grade girls, 33,188 10th-grade boys, 33,588 12th-grade girls, and 31,014 12th-grade boys participated in the study. The students completed self-administered, machine-readable questionnaires during a normal class period. The dependent variables focused on the proportion of students who used tobacco, alcohol, and a variety of illicit drugs in their life-time, in the last 30 days, and on a daily basis. An additional cigarette measure examined the proportion of students who smoked a half-pack or more of cigarettes per day; and an additional alcohol measure focused on heavy use (five or more drinks in a row, in a single sitting, within the last 2 weeks). The key independent measures were gender and ethnic identification. The study found that across ethnic groups, drug use was highest among Native-American girls and lowest among Black and Asian-American girls. Trend data suggest that there have been important changes in girls' drug use over time and that girls' and boys' drug-use patterns are converging. Future research should further examine girls' drug use and determine whether risk and protective factors identified in past research, based on predominantly White samples, are also important predictors for drug use among non-White girls. 4 tables, 1 figure, and 22 references