This work analyses the maximum and minimum temperatures and the precipitation series of four localities in Piedmont. Measurements regarding the stations of Torino, Asti, Vercelli and Oropa have been extracted from the meteorological database of the ex-SIMN (Hydrographic and Mareographic National Service). The values in the period 1990-2003 have been compared with the measurements carried out at the ARPA (Regional Agency for Environmental Protection)-Piedmont stations located about in the same place, in order to assess they similarity and possibly join the series. For each series, an historical investigation has been performed, and the homogeneity has been evaluated using the Standard Normal Homogeneity Test (SNHT). The results evidence some discontinuities among the data recorded by each couple of stations located in the same place, for both temperatures and precipitation. These discrepancies between the measurements underline the importance of using the homogeneity tests. The homogeneized meteorological series have been converted by the SNHT in a good instrument for estimating the trends and the real climatic changes.