This project addresses the need for practical and accurate assessment of vitamin and mineral supplement use in studies of nutrient intake and disease. With the recent focus on anti-oxidants, there is increasing emphasis on the role of vitamin and mineral supplements in chronic disease prevention. Epidemiologic studies commonly use self-administered questionnaires to collect information on nutritional supplement use. Typically, the respondent reports the general type of multivitamin or individual nutrient supplement and frequency of use. Remarkably little attention has been paid to the validity of supplement intake data obtained by these simple self-administered questionnaires. There is now some urgency to assess the accuracy of these questionnaires, motivated in part by the unexpected mortality associated with beta-carotene supplements in the Finnish chemoprevention trial. Given the widespread availability and use of supplements, precision in measuring their use will be an important components of assuring participant safety in dietary intervention and chemoprevention trials. The primary aim of this study is to evaluate the validity of three approaches to assessing nutritional supplement intake: (1) a telephone administered questionnaire, (2) a self-administered questionnaire, and (3) an interviewer administered assessment based on review of supplement bottles. Nutrient measures obtained via these methods will be correlated with nutrients from a gold standard; precise dose information transcribed from supplement labels. We will also evaluate the impact of these three different methods of assessing supplement use on misclassification of total nutrient intake (diet plus supplements), since this is typically the exposure of interest in studies of diet and disease. We propose to collect information on vitamin and mineral supplement use from 117 supplement users. We will recruit a community sample by phone, and administer a telephone questionnaire on supplement use asking participants to respond from memory. We will mail participants a packet of self-administered forms, including a short demographic questionnaire, a Food Frequency Questionnaire, and the self-administered supplement form. We will invite participants to the Cancer Prevention Studies Center for quality control review of the completed questionnaires, and ask them to bring supplements for the interviewer administered computerized assessment and label transcription. This research will provide important information on the relative accuracy of different ways to measure supplement use of participants in epidemiologic studies, and dietary intervention and chemoprevention trials.