Why do some people withdraw from biobank studies? To our knowledge, very few studies have been done on the reflections of biobank ex-participants. In this article, we report from such a study. 16 years ago, we did focus group interviews with biobank participants and ex-participants. We found that the two groups interestingly shared worries concerning the risks involved in possible novel uses of their biobank material, even though they drew opposite conclusions from their worries. Revisiting these interviews today reveals a (...) remarkable relevance to present concerns, since the possible developments that worried ex-participants and participants 16 years ago now are becoming realities. Drawing on conceptual distinctions by sociologist and philosopher Niklas Luhmann, we argue that while ex-participants express a loss of trust in the biobank institution to manage the use of their biobank material in a legitimate way, remaining participants expressed confidence in the management of the biobank institution to secure their interests. This analysis brings out important aspects of emerging trends in biobank research participation. (shrink)