Background: To interpret microarray experiments, several ontological analysis tools have been developed. However, current tools are limited to specific organisms. Results: We developed a bioinformatics system to assign the probe set sequences of any organism to a hierarchical functional classification modelled on KEGG ontology. The GeneBins database currently supports the functional classification of expression data from four Affymetrix arrays; Arabidopsis thaliana, Oryza sativa, Glycine max and Medicago truncatula. An online analysis tool to identify relevant functions is also provided. Conclusion: GeneBins provides resources to interpret gene expression results from microarray experiments. It is available at http://bioinfoserver.rsbs.anu.edu.au/utils/GeneBins/ Background Microarrays enable us to study the expression of thousands of genes simultaneously, providing a comprehensive overview of the gene activities in a given tissue. A number of ontological tools are now available that s...