In sunflower, commercial hybrid breeding is based on a single CMS inducing cytoplasm, the so-called PET1 cytoplasm. The introduction of one dominant, nuclear-encoded restorer gene (Rf1) is in most cases sufficient for fertility restoration. Little has been learned so far about the mode of action of the restorer gene Rf1. For map-based cloning of the restorer gene Rf1, an F2 population of the cross RHA325 (cms) x HA342 has been used. The χ²-test confirmed segregation for one dominant gene which corresponds to Rf1. For the AFLP analyses 256 EcoRI/MseI primer combinations have been used so far. In addition, RAPD analyses were performed using 1,200 decamer primers. Twenty-three primers had polymorphic amplification products, differentiating the bulks, and could therefore be mapped. The hybridization of the marker HP4 against a BAC library resulted in three positive clones. The overlapping end of the smallest clone was used to get a new hybridization against the BAC library.