Background. The 1985 Minnesota Legislature established guidelines for school-based tobacco-use prevention programming and provided financial incentives to school districts to encourage them to adopt a broad range of preventive measures. The Minnesota-Wisconsin Adolescent Tobacco-Use Research Project was funded by the National Cancer Institute in 1986 to evaluate the Minnesota initiative through two parallel studies. Methods. The Four Group Comparison Study was a prospective study of 48 school "units" which were randomly assigned to one of four conditions in 1987. Baseline observations were taken in the sixth grade in 1987, interventions were delivered in the seventh grade, and follow-up observations were taken in the seventh, eighth, and ninth grades. The Four Group Comparison Study was designed to evaluate the three middle-school interventions that were most widely adopted by Minnesota school districts as a result of the 1985 legislation. The Two State Comparison Study was a serial cross-sectional study of representative districts in Minnesota and Wisconsin. Annual surveys of ninth graders were conducted from 1986-1990. The Two State Comparison Study was designed to determine whether tobacco-use patterns changed in Minnesota relative to Wisconsin following the Minnesota legislation. Results. The prospective study indicated that none of the interventions was more effective in reducing adolescent tobacco use compared with a randomized control group. The serial cross-sectional study revealed that there was a modest net decline in Minnesota relative to Wisconsin from 1986 to 1990, but that it was within the range of chance variation. Conclusions. Taken together, these results indicate that this legislative initiative was insufficient to reduce adolescent tobacco use statewide during the 5-year study period. Together with results from other recent studies, they suggest that even more intensive efforts may be required to effect widespread reductions in adolescent tobacco use.