The co-ordination of expression of anthocyanin biosynthetic genes was studied in developing flowers. Four genes encoding enzymes operating late in the anthocyanin biosynthetic pathway are induced together during flower development but the early steps appear to be induced more rapidly. Co-ordination of expression could imply a common regulatory mechanism controlling the expression of metabolically related genes. The data presented here show that while four genes may share such a mechanism for the control of their expression during flower development, different control processes regulate the early steps of the pathway. Spatially, gene expression is patterned across the flower and appears to be very similar for all the biosynthetic genes. However, the observed influence of the regulatory gene Delila shows that the spatial co-ordination of gene expression must involve more than one regulatory system. Delila itself appears to have a dual function, being required for activation of expression of the later genes in the flower tube but repressing chalcone synthase gene expression in the mesophyll of the corolla lobes. It is postulated that common signals induce the expression of genes in the pathway during flower development. The data presented here suggest that the same regulatory mechanism interprets these signals for four of the genes encoding the later biosynthetic enzymes, but that different or modified mechanisms interpret the signals to control expression of chalcone synthase and chalcone isomerase genes in Antirrhinum flowers.