Summary Transcription factors containing a conserved DNA-binding domain similar to that of the proto-oncogenec-mybhave 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 thatArabidopsis thalianacontains more than 100R2R3-MYBgenes. 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 differentA. thaliana R2R3-MYBgenes have been obtained. Sequence comparison revealed conserved amino acid motifs shared by subgroups ofR2R3-MYBgenes in addition to the characteristic DNA-binding domain. No significant clustering of the genes was detected, although they are not uniformly distributed throughout theA. thalianagenome.R2R3-MYBgene expression levels were determined under more than 20 different growth conditions including hormone treatment, infection with pathogens and various stress conditions.MYBgenes are specifically expressed in different tissues and physiological conditions, indicating the potential for involvement in various regulatory processes. The sequence and expression data together with the map positions of nearly allMYBgenes inA. thalianaprovide a substantial basis for further studies of this important group of transcription factors.