Solar elastosis is a hallmark of photoaged human skin and a prominent feature in experimentally produced photoaging in murine skin. The products of mast cells have been implicated in the development of photoaged skin. We evaluated whether products from mast cells mediate chronic UVB-induced changes in murine skin by employing a strain of mast cell-deficient mice, WWv. The responses in these mice were compared to those in BALB/c, another albino mouse strain. Mice were exposed three times per week to UVB radiation for 11 weeks; the total dose was 18.8 J/cm2. Irradiated WWv mice showed greater epidermal alterations than the irradiated BALB/c mice. In the dermis, a 3.6-fold increase in elastin content, as measured by desmosine, was produced in the UVB-treated BALB/c mice; in contrast, no difference was observed in elastin between UVB-treated and untreated WWv mice. Collagen content was not increased by UVB treatment in either strain, and the glycosaminoglycan content increased a similar amount in UVB-treated mice in both strains. The number of mast cells increased two-fold and the number of neutrophils increased six-fold in UVB-treated BALB/c mice compared to age-matched unirradiated controls. Neutrophils, as well as mast cells, were absent in untreated and UVB-treated WWv mouse skin. These results suggest that products of mast cells are important in the development of solar elastosis in murine skin either by directly inducing elastin production by fibroblasts or indirectly by mediating the presence of other cell types that produce products that increase fibroblast elastin production.