The problem of reconstruction of daytime nonmonotonic height profiles of electron density N(h) from ionograms of ground-based vertical sounding is considered. The regularization (REG) scheme has been proposed for determination of valley parameters. A comparison of the least squares method (LSM) with the regularization (REG) scheme was carried out using computer simulations. It is shown that LSM results are very sensitive to random errors in virtual heights. This fact leads to an unpredictably large deviation of the reconstructed N(h) profile from the real one. The application of REG methods makes the results more stable to random errors in measurements and allows us to decrease the deviation of the restored real height and valley depth from their model values by several times in comparison with LSM results.