Abstract: This paper describes a conversational mass spectral search system which issuitable for microcomputer or minicomputer and runs on PDP-11/34A computer.It permits user to set up a special mass spectral library for various organiccompounds. The software consists of a library generation program and a lib-rary search program. These programs were written by PDP-11 FORTRANIV-PLUS language, and is easy to transfer to other computers. The librarygeneration program is used to produce a data file for simplified mass spectraand a index file for searching. In order to keep integrity of a library, theprogram was designed to have some additional functions, such as inserting,modifying, deleting, examining etc. The library search program used imme-diate and dual searching techniques and had seven pattens for searching. Thesearch system was applied to identify some special toxic and volatile compoundsin food, the results were satisfactory.