A positive regulatory element directing maximal expression of the Antirrhinum majus chalcone synthase promoter was characterized by protein-DNA-interaction studies and cis deletion analysis. The positive regulatory element consists of a 47 base pair direct repeat between positions -564 and -670 and provides three binding sites for nuclear protein factors from Nicotiana tabacum and Antirrhinum majus. Oligonucleotide competition assays revealed that the same factor(s) interact(s) with all three binding sites. Transient expression of chimeric chalcone synthase-neomycin phosphotransferase II genes in parsley protoplasts demonstrated that both halves of the 47 base pair repeat element are required for its in vivo function. A possible role of redundant binding sites for the positive regulatory function of the 47 base pair repeat element is discussed.