The pairfam study offers the rare opportunity of conducting dyadic analyses of partner and of parent-child relationships. Not only the randomly drawn anchor respondents are surveyed in the study, but also – with the consent of the anchors – their partners, parents and children. However, we must ask whether or in how far the participation of the secondary respondents is selective, thus introducing a nonresponse bias in the dyadic data. This article analyses what factors influence the participation of partners and parents of the anchors on the German Family Panel pairfam. We focus on the question of whether the quality of the relationship between the anchor and partner or anchor and parent influences participation. Among parents there is both an influence of the relationship quality in the narrower sense and an influence of the closeness of the relationship with regard to contact and mutual support. By contrast, relationship quality appears to have a lesser significance for the participation of partners, whereas the degree of institutionalisation in the relationship has a major influence. The article aims to sensitise pairfam users to the possibility of a nonresponse bias in dyadic analyses and provides information on suitable handling of the data.