Until 1989 carrier detection in families with cystic fibrosis (CF) took place by means of linkage analysis with polymorphic DNA markers. This is an indirect method to demonstrate carriership. For linkage analysis it is often essential that there is patient material available. Since the identification of the CF gene, direct DNA analysis of the most frequent CF mutations is possible. This allows direct demonstration of carriership by means of DNA analysis in the majority of cases, without the necessity always to investigate family members. Carriership detection of persons not related to CF patients, for example partners of CF carriers, is with this method also possible. In cases where none of the frequent CF mutations can be found, linkage analysis may still prove helpful. In this article we demonstrate some clinical examples of carrier investigation.