Chronic exposure of human or murine skin to ultraviolet B (UVB) radiation alters dermal extracellular matrix composition and increases the number of mast cells and inflammatory cells. Experiments were designed to test the possible role of UVB-induced tumor necrosis factor-alpha in these photoaging changes based on reports that C3H/HeN, but not C3H/HeJ or Balb/c mice, produce excess TNF-alpha in response to UVB exposure. Pigmented C3H/HeN and C3H/HeJ strains were exposed to a total of 75 J/cm2 of UVB radiation, and unpigmented Balb/c mice were exposed to 19 J/cm2. The UVB-induced increases in collagen, glycosaminoglycans, and neutrophil number were similar or the same in all three strains. The elastin increase was greater in C3H/HeJ than in C3H/HeN mice. The most striking difference between the strains was a 7.7-fold UVB-induced increase in mast cells in C3H/HeN mice compared to no increase in irradiated C3H/HeJ mice and a 2.3-fold increase in Balb/c mice. These results suggest that excess TNF-alpha (or other mediator) produced in C3H/HeN skin (but not C3H/HeJ skin) in response to UVB exposure is involved in the mast cell increase and partial inhibition of elastin increase, but that neither these mediators nor mast cell products are important mediators for the chronic UVB-induced increases in neutrophils, glycosaminoglycans, and collagen. When a possible source of the excess TNF-alpha was investigated, it was found that isolated epidermal cells from all three strains produced increases in TNF-alpha in response to UVB radiation. These results, as well as the previous results showing differences between these strains in UVB-induced effects on cutaneous immune function, are consistent with a model in which UVB-induced mediators from the epidermis stimulate another cell type to produce excess TNF-alpha (and other mediators) in the C3H/HeN but not C3H/HeJ or Balb/c mice.