Alternative splicing is an important cellular mechanism that increases the diversity of gene products. The number of alternatively spliced genes reported so far in plants is much smaller than that in mammals, but is increasing as a result of the explosive growth of available EST and genomic sequences. We have searched for all alternatively spliced genes reported in GenBank and PubMed in all plant species under Viridiplantae. After careful merging and manual review of the search results, we obtained a comprehensive, high-quality collection of 168 genes reported to be alternatively spliced in plants, spanning 44 plant species (March 22, 2003 update). We developed a relational database with Web-based user interface to store and present the data, named the Plant Alternative Splicing Database (PASDB), freely available at http://pasdb.genomics.org.cn. We analyzed the functional categories that these genes belong to using the Gene Ontology. We also analyzed in detail the biological roles and gene structures of the four genes that are known to be alternatively spliced in more than one plant species. Finally, we studied the structural features of the splice sites in the alternatively spliced genes.