STUDY OBJECTIVE--The study aimed to determine whether asking women to undertake an additional scientific study would deter them from attending screening for breast cancer. DESIGN--A randomised study was conducted in all women aged 50-70 years who were eligible for breast cancer screening and living in the city of Utrecht. A total of 1863 women were invited for mammography only and 1863 women were invited to participate in the European Prospective Investigation into Cancer and Nutrition (EPIC) in addition to the mammography. SUBJECTS--The study population comprised a random sample of 3726, 15% of the female population of Utrecht aged 50-70 years. MAIN RESULTS--The attendance rate for breast cancer screening was 53%, irrespective of the invitation to participate in the additional scientific study. CONCLUSIONS--Asking women to attend for an investigation in addition to the routine screening procedure for breast cancer did not affect the overall response to screening.