Arabidopsis is a model system not only for studying numerous aspects of plant biology, but also for understanding mechanisms of the rapid evolutionary process associated with genome duplication and polyploidization. Although in animals interspecific hybrids are often sterile and aneuploids are related to disease syndromes, both Arabidopsis autopolyploids and allopolyploids occur in nature and can be readily formed in the laboratory, providing an attractive system for comparing changes in gene expression and genome structure among relatively 'young' and 'established' or 'ancient' polyploids. Powerful reverse and forward genetics in Arabidopsis offer an exceptional means by which regulatory mechanisms of gene and genome duplication may be revealed. Moreover, the Arabidopsis genome is completely sequenced; both coding and non-coding sequences are available. We have developed spotted oligo-gene and chromosome microarrays using the complete Arabidopsis genome sequence. The oligo-gene microarray consists of ~26 000 70-mer oligonucleotides that are designed from all annotated genes in Arabidopsis, and the chromosome microarray contains 1 kb genomic tiling fragments amplified from a chromosomal region or the complete sequence of chromosome 4. We have demonstrated the utility of microarrays for genome-wide analysis of changes in gene expression, genome organization and chromatin structure in Arabidopsis polyploids and related species.