This study examined the direct and mediated impact of a self-administered, computer-based intervention on nutrition behavior self-efficacy, and outcome expectations among supermarket food shoppers. The intervention, housed in kiosks in supermarkets and based on social cognitive theory, used tailored information and self-regulation strategies delivered in 15 brief weekly segments. The study sample (N = 277), stratified and randomly assigned to treatment or control, was 96% female, was 92% White, had a median annual income of about $35,000, and had a mean education of 14. 78 +/- 2.11 years. About 12% of the sample reported incomes of $20,000 or less, and about 20% reported 12 years or fewer of education. Analysis of covariance immediately after intervention and at a 4- to 6-month follow-up found that treatment led to improved levels of fat, fiber, and fruits and vegetables. Treatment also led to higher levels of nutrition-related self-efficacy, physical outcome expectations, and social outcome expectations. Logistic regression analysis determined that the treatment group was more likely than the control group to attain goals for fat, fiber, and fruits and vegetables at posttest and to attain goals for fat at follow-up. Latent variable structural equation analysis revealed self-efficacy and physical outcome expectations mediated treatment effects on nutrition. In addition, physical outcome expectations mediated the effect of self-efficacy on nutrition outcomes. Implications for future computer-based health promotion interventions are discussed.