The concentrations of 90Sr at different depth levels have been determined in 55 soils from 11 points at Biscay (Spain) by extracting this radionuclide from 30 g samples. It was measured by beta-counting after purification. The concentrations of 137Cs in the same soils are known from previous studies. Soils were also characterised by sampling depth, particle size analysis and the usual chemical parameters. The 91Sr activity concentrations in the studied soils ranged from 0.28 to 9.10 Bq/kg, with an average value of 2.85 Bq/kg. The more frequent behaviour in a depth profile is a continuous decrease of 90Sr. The dependence of 90Sr activities on soil parameters and 137Cs concentration are discussed by statistical methods, mainly by correlation coefficients, cluster analysis and non-linear regression of the accumulated radionuclide with depth. By this technique an estimation of fallout can be made. The ratio of the estimated deposition rate for both nuclides had values in the range from 0.72 to 5.82. This variation is related to soil constituents.