Previously, we reported two DNA repair-defective siblings who did not belong to any complementation group of xeroderma pigmentosum (XP) or Cockayne syndrome (CS). By surveying other photosensitive patients whose fibroblasts showed similar biochemical phenotypes, we found another nonconsanguineous Japanese patient belonging to the same complementation group as our previous cases. Postreplication repair of the cells derived from these patients was normal, indicating that they cannot be classified as XP variant. Neither transfection nor microinjection of the cells with the human DNA repair gene ERCC1, which is known not to correct any complementation groups of XP or CS, failed to correct the defect of these cells, indicating that they do not belong to the rodent complementation group 1. However, the defect in recovery of RNA synthesis (RRS) after UV irradiation was restored by microinjection of HeLa cell extract. Although clinical manifestations of these patients--such as acute sunburn, dryness, freckling, pigmentation anomalies on sun-exposed skin, and teleangiectasia without neurological abnormalities or tumors--are similar to a mild XP phenotype, cellular characteristics such as UV sensitivity and defective RRS after UV irradiation with normal unscheduled DNA synthesis (UDS) are reminiscent of CS. On the basis of these results, we propose that these patients be included under a general category designated "UV-sensitive" (UVs) syndrome.