APASdb provides information on Alternative Poly(A) (APA) isoforms for all genes. It describes heterogeneous cleavage sites downstream of poly(A) signals, and maintains near complete coverage for APA sites. APASdb provides the quantification of a given APA variant among transcripts with different APA sites by computing their corresponding normalized-reads. In addition, APASdb supports URL-based retrieval, browsing and display of exon-intron structure, poly(A) signals, poly(A) sites location and usage reads, and 3'-untranslated regions (3'-UTRs). Currently, APASdb involves APA in various biological processes and diseases in human, mouse and zebrafish.