OBJECTIVES: Understanding attitudes to mental health issues can inform public health interventions. However, low response rates may contribute to nonresponse bias. In a randomized controlled trial we examined the effect of sending a prenotification postcard before the questionnaire and the placement of a short message on the survey envelope (teaser) on response rates to a mailed questionnaire about bulimia nervosa "mental health literacy". STUDY DESIGN AND SETTING: Questionnaires were mailed to 3,010 adults (50.6% female and 49.4% male) aged 18-65 years. In a 2 (pre-notification-present; absent) by 2 (teaser-present; absent) design, questionnaire recipients were randomly allocated to the experimental strategies. Outcomes considered were response rate, response time, and cost. RESULTS: The overall response rate was 22.0%. Significant main effects showed higher response rates for the use of prenotification (present = 23.6%; absent = 20.3%), among female participants, and older participants. A significant interaction of teaser by gender indicated lower response rates for men who received the teaser but not for women. Older participants returned the questionnaire more promptly than younger participants. Females-but not males-who received the teaser were slower to return the questionnaire. Higher response rates for participants receiving the postcard compensated for increased costs, particularly for males and older participants. CONCLUSION: Response rates to a mental health postal survey can be increased through the use of prenotification.