The evaluation of stability of natural slopes in residual soils involves in many cases a considerable degree of uncertainly due to the difficulty of estimating or knowing the pore pressure operating in the slope. Much less uncertainly however existis in determining the effective strength parameters for the soils involved. This work deals with the evaluation of pore pressures through back-analysis of brazilian case histories. In order to do partial loss of suction that are caused bu the infiltration of rain water. A report on the tests conducted in the laboratory is presented as well as a survey on shear strength parameters of residual soils. A study on suction in soils is also presented with enphasis in the relationship moisture- suction. Seven case histories were chosen in order to carry out the back-analysis. In these cases there was available and reliable information on the geometry of the failure surface and shear strength parameters. The strength envelope proposed by Fredlund et all (1978) for partially saturated soils and conventional strength envelope for saturated soils were used in the analysis. The simplified Bishops method was used for circular failure surfaces while Jambus simplified method was used for non-circular surfaces parallel to the slope surface. In four of the case histories analysed, negative mobilized pore pressures were found showing that the intability could be associated only to the reduction in suction. In two other cases the average pore pressure were slightly positive while in the last three cases, positive. A study has been carried out to investigate the possible effect of pore pressure distribution with depth on the stability analysis. The results did not alter the main conclusion of the study, i.e., at failure in these case histories pore suctions of low pore water pressures were generally operating.