CINEMA is a new editor for manipulating and generating multiple sequence alignments. The program provides both an interface to existing databases of alignments on the Internet and a tool for constructing and modifying alignments locally. It is written in Java, so executable code will run on most major desktop platforms without modification. The implementation is highly flexible, so the applet can be easily customised with additional functions; and the object classes are reusable, promoting rapid development of program extensions. Formerly, such extended functionality might have been provided via browser plug-ins, which have to be downloaded and installed on every client before loading data. Now, for the first time, an applet is available that allows interactive client-side processing of an alignment, which can then be stored or processed automatically on the server. The program is embedded in a comprehensive help file and is accessible both as a stand-alone tool on UCL's Bioinformatics Server; http:/(/)www.biochem.ucl.ac.uk/bsm/dbbrowser+ ++/CINEMA2.02/, and as an integral part of the PRINTS protein fingerprint database. Exploitation of such novel technologies revolutionises the way users may interact with public databases in the future: bioinformatics centres need not simply provide data, but are now able to offer the means by which information is visualised and manipulated, without the requirement for users to install software.