A new test method is presented to quantify the thermal diffusivity, devised for on-site non-destructive measurements of solids accessible from one side only.A periodic thermal disturbance is supplied to the inspected solid by a thermoelectric unit based on the Peltier effect. This can alternate heating and cooling stages and provide, if properly controlled, a null net heat flux. A steady-periodic temperature field can be quickly produced within the solid. The diffusivity of the material is then estimated by monitoring the propagation of the temperature cycles along the optically accessible surface of the solid, adjacent to the thermal input surface area. A portable camera for infrared thermography is used for non-intrusive surface temperature measurement.Tests on thermally thin specimens of materials with well known properties give measures in encouraging agreement with the nominal values.At the current stage of development, the attention is focused onto obtaining the adherence of the test system to the theoretical model on which the method is based. Ease of operation and portability of the testing equipment are also pursued.