Forty-two samples of soils from Spain, corresponding to the principal humus types, were studied by direct Py-GC. The matrix formed by the area of twenty-five selected peaks of each pyrogram from 42 soil samples were considered as data base for the factor analysis. The analysis between peaks shows positive correlations between pyrolysis products having the same origin. The nitrogen-containing products and some aromatic hydrocarbons are negative correlated to the carbohydrate derivatives and to some phenolic pyrolysis fragments. In the analysis between soils, the anaerobic humus types and the carbonated mulls are well discriminated. By contrast, moders and acid mulls humus are overlapped in this analysis. © 1987.