In this review some aspects of DNA photochemistry are presented. In particular the interest is devoted to the study of the conformational changes due to the photoproducts iduction (pyrimidine cyclobutane dimers and (6-4) photoadducts). This study is connected with the interpretation of repair mechanisms at cellular level. In fact, it is known that the enzymatic repair occurs by means of the recognition of locally distorted sites in DNA structure. In the second place, given the particular interest devoted in recent years to the effects of UV-B (present in the solar spectrum), the phenomenon of photosensitization is considered. The specific effect of some metal ions, present as trace in cells, is shown to be a damage enhancement due to the modified spectral properties of DNA.