Expression profiling by cDNA-AFLP is commonly used to display the transcriptome of a specific tissue, treatment or developmental stage. In this paper, cDNA-AFLP has been used to study transcripts expressed in segregating populations from Arabidopsis thaliana and potato (Solanum tuberosum). The genetic differences between the offspring genotypes are thus visualized as polymorphisms in the transcriptome. We show that polymorphic transcripts can be used as genetic markers and allow the construction of a linkage map. The resulting map shows that, in contrast to genomic markers, the transcriptome-derived markers did not cluster in particular areas of the chromosome, and that cDNA-AFLP markers are targeted specifically to transcriptionally active regions. The cDNA-AFLP markers used in mapping are derived from DNA polymorphisms in transcripts, rather than differences in expression regulation. The high potential of transcriptome markers as opposed to (anonymous) genomic markers for applications in genetic analyses, marker-assisted breeding and map-based cloning is discussed.