OBJECTIVE: To determine the effectiveness of an intervention Tool Kit of arthritis self-management materials to be sent once through the mail, and to describe the populations reached. METHODS: Spanish speakers (n = 335), non-Hispanic English-speaking African Americans (n = 156), and other non-Hispanic English speakers (n = 404) were recruited separately and randomized within each of the 3 ethnic/racial categories to immediately receive the intervention Tool Kit (n = 458) or to a 4-month wait-list control status (n = 463). At the end of 4 months, controls were sent the Tool Kit. All subjects were followed in a longitudinal study for 9 months. Self-administered measures included health status, health behavior, arthritis self-efficacy, medical care utilization, and demographic variables. Using analyses of covariance and t-tests, analyses were conducted for all participants and for Spanish- and English-language groups. RESULTS: At 4 months, comparing all intervention subjects with randomized wait-list controls, there were significant (P < 0.01) benefits in all outcomes except medical care utilization and self-rated health. The results were maintained at 9 months compared with baseline. On average, the Tool Kit reached persons ages 50-56 years with 12-15 years of schooling. There were few differences between English- and Spanish-language participants in either the effectiveness or reach variables. CONCLUSION: A mailed Arthritis Self-Management Tool Kit proved effective in improving health status, health behavior, and self-efficacy variables for up to 9 months. It also reached younger persons in both English- and Spanish-language groups and Spanish speakers with higher education levels than previous studies of the small-group Arthritis Self-Management Program.