A simple mechanical model in which the response of the lithosphere to loading was approximated by a semi-infinite (broken) elastic plate overlying a weak fluid was used to analyze the deflection of the foreland lithosphere beneath the Apennine and outer East Carpathian foredeep basins. Comparison between the calculated and observed depth to basement suggests that the emplacement of thrust sheets onto the foreland lithosphere during mountain building failed to produce a sufficient load to create the foredeep basins and topography regardless of the position of the slab end or the flexural rigidity assumed for the foreland lithosphere. We infer that an additional subsurface load must be present and that its magnitude must be roughly equal to the load created by that part of the thrust belt that is above sea level. For the two Apennine transects, an acceptable fit to the shape and size of the observed foredeep basin was generated by assuming effective elastic plate thickness of 8 and 15 km (4.9 and 9.3 mi) and applied vertical forces of 2 X 10 15 dynes/cm and 1.3 X 10 15 dynes/cm at the slab end. For the Carpathian transect, an effective plate thickness of 30 km (18.6 mi) and an applied force of 1.5 X 10 15 dynes/cm generated an acceptable fit. This study suggests a method whereby an estimate of the depth to autochthonous basement rocks beneath overthrust belts can be made. Such an approach may enable exploration geologists to determine if crystalline rocks encountered in drilling overthrust terranes are a part of the autochthonous basement, or if they are part of an overthrust sheet.--Modified journal abstract.