A very moderate, non-destructive radioactivation of oil paintings,induced by thermal neutron bombardment, such that approximately only one in 10¹² of the atoms comprising any painting is transformed into a radioactive species, has been found to produce temporary radioactivity sufficient to expose photographic film placed in direct contact with the paintings. The resulting autoradiographs resemble conventional X-radiographs in that they reveal structural details in depth of both the painting and its support. Since the radioactivities arising from the different elements within a painting decay in different manners and at different rates, a series of significantly distinct autoradiographs can be obtained of any painting by making exposures through ap propriate filters and at varying times following the original activation. Analysis of such a series of autoradiographs permits the identification of a number of the pigments used in a painting, together with information about the manner in which they were originally laid down by the artist and their distribution throughout the body of the painting. Preliminary investigations have shown that the stability of oil paintings is unaffected by the activation procedure. The inherently necessary radiation dose absorbed by a painting as a result of activation sufficient for autoradiography is of the order of 50 rads. Paintings subjected to absorbed doses one hundred times as great as the dose necessary for autoradiography exhibit no changes in color, hardness, flexibility and solubility three years after their original -- AATA