​As in other scientific branches, the increase of the avaiable petrologic and geochemical data and the multiple studies that can be developed lead to the exploitation of computer facilities. On this domain, data base systems and processing applications are of great importance. This paper reports the main characteristics of GEOPACK (version 3.0), a GWBASIC package for IBM or compatible microcomputers aimed to treat petrological and geochemical data. Besides applications of general use, it contains routines directed to the classification of igneous rocks, the characterization of magmatic series, the production of variation diagrams, the study of isotopic ratios, the drawing of tectonomagmatic discrimination diagrams and the application of geothermometers.