MOTIVATION: Regulation of nuclear mRNA export or retention is carried out by RNA elements but the mechanism is not yet well understood. To understand the mRNA export process, it is important to collect all the involved RNA elements and their trans-acting factors. RESULTS: By hand-curated literature screening we collected, in ExportAid database, experimentally assessed data about RNA elements regulating nuclear export or retention of endogenous, heterologous or artificial RNAs in mammalian cells. This database could help to understand the RNA export language and to study the possible export efficiency alterations owing to mutations or polymorphisms. Currently, ExportAid stores 235 and 96 RNA elements, respectively, increasing and decreasing export efficiency, and 98 neutral assessed sequences. AVAILABILITY AND IMPLEMENTATION: Freely accessible without registration at http://www.introni.it/ExportAid/ExportAid.html. Database and web interface are implemented in Perl, MySQL, Apache and JavaScript with all major browsers supported.