Site data from 291 forest inventory plots in Mixed Dipterocarp Forest in central Sarawak were simplified by factor analysis. The distribution of the 33 commonest canopy tree species was related to site factor scores by ‘t’ tests. There appears to be a degree of edaphic influence on the distribution of many species. Fairly constant soil characteristics related to the lithology of the parent material appear to be more important than ephemerally variable pro perties such as organic matter or exchangeable cations. Magnesium appears to be particularly important, possibly because of an effect on the capacity of mycorrhizal root systems to absorb phosphorus.