ABSTRACTSoil loss was measured in Kiambu District during the long rainy season, 1982. From the data gathered during this period, the USLE was calibrated for the agro-ecologic conditions existing in the area. During 1983, soil loss measurements were collected in Murang'a District for the two growing seasons. Using the Kiambu calibrated USLE values, soil loss was estimated also for Murang'a. The significant correlation between the estimated and measured soil loss values indicates that the USLE, as calibrated for Kiambu, gives meaningful estimates in this area of Kenya. Nevertheless, the estimation of the erosivity values at the field level as well as the assessment of the conservation practices need further refinement.The measured soil loss values in both districts indicate that fields in annual crops, especially cotton and maize, result in the highest soil losses; perennial cash crops result in the lowest soil losses. It appears that approximately 25 % of the sampled fields are undergoing land degradation solely due to excessive soil losses. This is especially true in areas of recent agricultural expansion as they generally have higher soil losses than the established farming areas.