Genomic and cDNA clones of the chalcone synthase gene (chs) of Antirrhinum majus have been isolated and sequenced. By sequence comparison the structure of the gene was deduced. The coding region of the chs gene is interupted by two intervening sequences of 721 bp and 211 bp. The gene codes for a protein with a MW of 42,665 daltons. The start point of transcription was identified by S1 mapping and primer extension. Putative TATA and CAAT boxes are present in the 5′control region, and a polyadenylation signal, AATAAA, is found in the 3′untranslated region. Several unusual sequence motifs are present in the 5′flanking region. Their possible involvment in chs expression is discussed.