The rDNA probes 5.8S-18S-25S and 5S of sunflower (Helianthus annuus L., 2n=34) have been physically mapped on chromosome spreads by fluorescent in situ hybridization. The biotin-labelled 5.8S-18S-25S rDNA probe showed a strong hybridization signal on three pairs of satellited chromosome at sites corresponding to the active NORs, and on a pair of fainter, not previously reported sites. The digoxigenin-labelled 5S rDNA probe was found to hybridize on two sites, one of which lies on a satellited chromosome