Measurements of radon's concentration have been effected in the schools of two communes of Puglia: Polignano and Valenzano. The average concentration of radon, based on the prospecting effected in the research period (spring/summer 1997), appeared, for both communes, lower than national average (75 Bq/m3). However, these average concentrations is below estimated caused of the limitation of the research period, owing to organization only at the period spring/summer. In fact, by the extrapolation applying a right factor of conversion, of the "winter" average concentrations from that average calculated during the research period (considering the evident limits of such procedure) we obtain, respectively, for both schools of Polignano and Valenzano, an average concentrations about of 75 Bq/m3 e 103 Bq/m3. The research shows the existence of a correlation among the obtained results and two important factors: the buildings materials utilized and the geological conformation of the subsoil; in particular, the buildings having main wall (tufa) or built by mixed materials (cement, bricks and tufa) measured the highest radon concentrations. Nevertheless, the absolute risk to develop a pulmonary tumour due to the radon exposition, limitedly for the population of the common of Valenzano, appears lightly superior in respect of the national risk (6 cases on 100,000 fellows) resulted about 8.5 case on 100,000 fellows.