The Petunia hybrida mutant RL01 is white flowering due to a genetic block in the anthocyanin pathway. The introduction of the maize A1 cDNA under the control of the CaMV 35S RNA promoter leads to the production of pelargonidin derivatives, resulting in a brick red flower phenotype. Among the transgenic petunia plants the pigmentation of the petals exhibited different expression patterns which could be categorized into the 'red', the 'variegated', and the 'white' phenotype. This system proved to be especially suitable for the investigation of gene expression by simply looking at the pigmentation pattern of the petals. The uniformity of floral pelargonidin pigmentation is inversely correlated with the number of integrated A1 copies. Furthermore, a correlation was found between the methylation status of the 35S RNA promoter and the instability of the floral pelargonidin coloration. The status of promoter methylation controlling the expression of the A1 gene seems to be influenced by the copy number and the chromosomal position of the transferred gene.