A dual mode facsimile data compression technique, called Combined Symbol Matching (CSM) , is presented. The CSM technique possesses the advantages of symbol recognition and extended run-length coding methods. In operation, a symbol blocking operator isolates valid alphanumeric characters and document symbols. The first symbol encountered is placed in a library, and as each new symbol is detected, it is compared with each entry of the library. If the comparison is within a tolerance, the library identification code is transmitted along with the symbol location coordinates. Otherwise, the new symbol is placed in the library and its binary pattern is transmitted. A scoring system determines which elements of the library are to be replaced by new prototypes once the library is filled. Non-isolated symbols are left behind as a residue, and are coded by a two-dimensional run-length coding method. Simulation results are presented for CCITT standard documents. With text-predominate documents, the CSM compression ratio exceeds that obtained with the best run-length coding techniques by a factor of two or more, and is comparable for graphics-predominate documents.