As DNA sequencing technology improves and more rapid techniques become routine in molecular biology labs, researchers need to expedite the incorporation of information into genetic sequence databases, such as GenBank, by directly submitting sequence data. The Annotator's Assistant is an expert system that runs on an IBM PC and helps the molecular biologist, who may have little knowledge of the structure or content of a GenBank entry, to construct a complete and valid sequence submission file. This expert system uses a simple molecular biology knowledge base and a selection of customized screen entry forms to guide the user through the entry and annotation of a sequence and its biological features. The system compiles information about the contributor, journal references, physical and functional characteristics of the nucleic acid, source organism and features, and checks it to eliminate incomplete answers and simple errors. Users supply input by answering direct and multiple-choice questions, selecting menu items and completing entry forms; on-line help is available. Users may also enter new or unusual information using generic forms. Several modules of the expert system were converted into Prolog programs and compiled, decreasing the running time significantly. The expert system rules and the data entry forms are easy to modify, update and customize for specific sequence classes.