At the ISB-Institut fur Jledizinische Informations- verarbeitung, Statistik und Biomathematik' in Munich our research group conducts pilot studies for a nationwide longitudinal study on side-effects of contraceptives. One of our objectives is to determine which topics can be investigated using population surveys. In 1975 we drew a random sample of the female population aged 12-45 years in the Munich area (n+639). This Pilotl sample was interviewed, using a standardized questionnaire. In 1976 and 1977 a self-completion questionnaire was mailed to the '75- sample' . The response to these questionnaires showed a marked dependency on the participation in the Project's medical examination program. Overall response rates, based on the initial sample, turned out to be: 81.4% in the second survey, 70.4% in the third survey.