Chrionic exposure of the skin UVB radiation causes erythema and dermal connective tissue damage including wrinkling, neoplastic skin lesions, and delayed wound healing. The topical application of epidermal growth factor(EGF) has been reported to be effective in the treatment of partial and full thickness skin wounds, second degree burns, incision wound, and chronic ulcers. However, its effect thickness UVB damaged skin has not yet been defined. Fifty Sprague-Dawley rats were divided into four groups: UV irradiated-EGF treated group; UV irradiated-EGF untreated group; UV nonirradiated-EGF treated group; UV nonirradiated-EGF untreated Group peroperatively, the UV exposure groups were irradiated with UVB (40 mJ/cm2, 2 MEDs) on the dorsal skin every other day for 12 weeks. Following cessation of UNB exposure, a standard 6 cm midline dorsal linear incision was made in each animal. The animals in EGF treated group were topically applicated with EGF ointment (10 microgramg/g) twice a day. Wounds were excised and wound burst strength was applicated using tensiometer on the 7th and 10th postwounding days. The wound burst strength of the UV irradiated-EGF treated group (662+/-49.7 g/cm) was significantly increased compared to that of the UV irradiated-EGF untreated group (352 +/-40.3 g/cm) (p < 0.01) and even stronger than that of the UV nonirradiated-EGF untreated group (570+/-44.7 g/cm) (p < 0.05). On the 10th day, there was no significant difference in the wound burst strength between the UV irradiated-EGF treated group (1248 +/-101.3 g/ cm) and UV nonirradiated-EGF treated group (1270+/-98.5 g/cm) (p = 0.595). Histological examination revealed epidermal hyperplasia, degeneration of collagen fibers, and inflammatory cell infiltration in the UV irradiated groups. Thick epidermis, prominent skin appendages, increased capillaries and fibroblasts, and linear organization of collagen fibers were observed in EGF treated groups. These results indicate that repeated exposure to UVB irradiation alters normal skin structure and adversely affects subsequent wound healing and the topical application of epidermal growth factor facilitates wound healing of UVB damaged skin.