Total physical activity scores, based on level of participation in 13 types of activities for 2658 black and white women aged 18 to 30 years were examined in relation to demographic, health behavior, psychosocial, and obesity data to compare levels of physical activity and determine reasons for disparities between blacks and whites. Black women had lower scores than white women--geometric mean of 178 (95% confidence interval (CI): 167, 189) versus 318 (95% CI: 305, 332). After controlling for age and education, physical activity was associated with physical activity level before high school, life events score, John Henryism, and competitiveness in both groups. In white women only, it was associated with alcohol intake and need to excel, and negatively associated with number of children, number of cigarettes smoked, and fatness. Race remained a predictor of physical activity after controlling for each variable. Relationships between physical activity and age, education, cigarette smoking, and life events differed significantly by race. Black women had lower physical activity levels than white women, which may contribute to higher rates of obesity and coronary heart disease. Racial differences in physical activity remain largely unexplained by the factors examined.