GABI-Kat SimpleSearch is a database of flanking sequence tags (FSTs) of T-DNA mutagenized Arabidopsis thaliana lines that were generated by the GABI-Kat project. Sequences flanking the T-DNA insertion sites were aligned to the A.thaliana genome sequence, annotated with information about the FST, the insertion site and the line from which the FST was derived. A web interface permits text-based as well as sequence-based searches for relevant insertions. GABI-Kat SimpleSearch aims to help biologists to quickly find T-DNA insertion mutants for their research.