APAlyzer is a toolkit for bioinformatic analysis of alternative polyadenylation (APA) events using RNA sequencing data. Our main approach is the comparison of sequencing reads in regions demarcated by high-quality polyadenylation sites (PASs) annotated in the PolyA_DB database (https://exon.apps.wistar.org/PolyA_DB/v3/). The current version (v3.0) uses RNA-seq data to examine APA events in 3’ untranslated regions (3’UTRs) and in introns. The coding regions are used for gene expression calculation.