Suppressive soils are defined as those soils in which plant disease development is suppressed by their biotic or abiotic characteristics. The objective of the present research is to evaluate soil supressiveness to a plant pathogen (Rhizoctonia solani) as an environment indicator. Sixty soil samples were collected from Taquara Branca watershed (Sumaré,SP). Soil samples collected from a native forest and pastures have shown greater supressiveness to R. solani than those from intensive crops. The results indicate the effect of crop systems on the soil equilibrium. The microorganisms of the soil are shown to be the main cause of supressiveness. The effect of several soil variables are discussed.1997