UV irradiation results in marked changes in skin connective tissue, such as degeneration of collagen, and abnormal elastosis. The mechanism of connective tissue damage by UV has not been clarified in detail. In the present study the mechanism of actinic damage was studied by assaying gelatinases, 72-kDa (MMP-2) and 92-kDa (MMP-9), from suction blister fluids induced on patients who had received either UVB or PUVA treatments. The results indicate that both UVB and PUVA increase the levels of gelatinases in human skin. By in situ hybridization, it was also possible to show that UV irradiation induced increased levels of gelatinase mRNAs in fibroblasts. Furthermore, in samples from severe actinic damage, gelatinase mRNAs were abundantly present, suggesting that gelatinases may contribute to photodamage.