In this paper, we try to understand the motivations and characteristics of people susceptible to be volunteers for the SU.VI.MAX study. The objective of this study will be to recruit and to follow during 8 years, a cohort of 15,000 subjects at a national level, for an intervention trial in the field of nutritional prevention. A short media campaign has been organised to recruit "1,000 volunteers to help to test and to validate tools specifically developed for the SU.VI.MAX study". In total, 15,789 subjects matching selection criteria answered to our invitation. All received a short questionnaire; 10,984 sent back correctly filled up questionnaires (70%) and 1005 were selected at random for a complete analysis. A lexical analysis of motivations disclosed 6 different groups organised in two poles. The pole of true altruists with a speech relative to notions such as "volunteers-benevolent" (7% of subjects), wishes to participate to a "humane task" (9% of subjects) or to progress of medical research (27% of subjects). The other pole corresponds to people interested personally by the theme of the project with 3 kinds of speech: personal past history (13% of subjects), interest for foods fortified with vitamins and/or minerals (19% of subjects) or for relationships between food consumption and health (22% of subjects).