Transcription factors containing a conserved DNA-binding domain similar to that of the proto-oncogene c-myb have been identified in nearly all eukaryotes. MYB-related proteins from plants generally contain two related helix-turn-helix motifs, the R2 and R3 repeats. It was estimated that Arabidopsis thaliana contains more than 100 R2R3-MYB genes. The few cases where functional data are available suggest an important role of these genes in the regulation of secondary metabolism, the control of cell shape, disease resistance, and hormone responses. To determine the full regulatory potential of this large family of regulatory genes, a systematic search for the function of all genes of this family was initiated. Sequence data for more than 90 different A. thaliana R2R3-MYB genes have been obtained. Sequence comparison revealed conserved amino acid motifs shared by subgroups of R2R3-MYB genes in addition to the characteristic DNA-binding domain. No significant clustering of the genes was detected, although they are not uniformly distributed throughout the A. thaliana genome.