A system has been developed to process data generated by a high-resolution mass spectrometer using a small computer. The computer is dedicated to the instrument only during data acquisition and is otherwise available for a variety of computational tasks in a general mass spectrometry laboratory. The programs include those to acquire the data directly from the mass spectrometer and store them on the computer disk storage device (written in assembly language); those to reduce the data on the disk to a table of exact masses and intensities, including deconvolution of multiplets (written in FORTRAN IV); and those to determine possible empirical formulas and fragmentation sequences for a given series of exact masses (also in FORTRAN IV). All observed PFK peaks are used as reference masses in an advancing subregion techinque that gives improved mass measuring accuracy.