AlterORF is a searchable database that contains information regarding alternate open reading frames (ORFs) for over 1.5 million genes in 481 prokaryotic genomes. The objective of the database is to provide a platform for improving genome annotation and to serve as an aid for the identification of prokaryotic genes that potentially encode proteins in more than one reading frame. The AlterORF Database can be accessed through a web interface at www.alterorf.cl.