One of the major methods of data collection used in both formative and outcome evaluations and descriptive studies is the survey method. With survey methods, the issues of generalizability and representativeness of the data are crucial, particularly when response rates are low. A common survey method is the use of mailed questionnaires, however, even when care is taken to select potential respondents randomly, the validity of the responses depends on the willingness of all sectors of the population to respond. In most instances, no effort is made to follow up individuals who do not respond, to ensure that they do not differ on substantive issues from individuals who have responded. The authors describe the process of following up university students who chose not to respond to a mail survey of their life-styles and drug use patterns, and a comparison of this group with a group of students who did respond to the initial request.