Chromatin-bound metal ions interact with enzymatic reactions involved in DNA repair processes. Content of Cu, Zn and Mn was studied in the chromatin of lymphocytes derived from patients with some light sensitive skin diseases, i.e. 26 with polymorphic light eruption and 10 with porphyria cultanea tarda. After isolating the lymphocytes by ficoll-urographin method and separating the chromatin by lysis of the cells, the trace elements studied were determined by neutron activation analysis. The Zn and Mn content in the chromatin of the patients did not differ from that of the controls. The copper concentration was significantly higher in the chromatin of the cells derived from patients with polymorphic light eruption, but not in cases with porphyria cutanea tarda. The results are discussed in connection with the UV-light induced excision repair.