Background. This paper examines participation rates and the association between participation and study outcomes (% energy from fat) among participants in the Women's Health Trial: Feasibility Study in Minority Populations, a randomized clinical trial to determine if ethnically and socioeconomically diverse women could be recruited and make significant dietary changes. Methods. Women (n = 2,208) were recruited from three clinical centers and randomized to either an intervention group or a control group. Multiple measures were collected at 6 months. Results. Participation rates for follow-up data collection activities were high (average participation 79%). Hispanics and lower educational groups participated significantly less (59% for Hispanics vs 86% for blacks and whites; 78% for lowest educational group vs 84% for highest educational group). Intervention participation significantly predicted change in percentage energy from fat (P < 0.001), accounting for an additional 8% of variance after background variables were controlled for. Conclusions. These data suggest that intervention participation is positively related to dietary change, but they cannot rule out the possibility that other factors may influence both of these factors. (C) 2000 American Health Foundation and Academic Press.