Earlier studies of ultraviolet (UV) irradiated hairless mice have suggested a relation between elastosis and mast cells. To examine whether such a relation exists, we examined groups of hairless mice irradiated with equal doses of UV. The narrow UV bands had peaks at 292, 300, 307, 317 and 336 nm. The groups were irradiated 5 times per week during 1 year. It was shown that the shorter the wavelengths, the more pronounced was the degree of elastosis. Sections from dorsal skin were prepared for light microscopy and stained with orcein, making it possible to detect the elastosis at the same time as the mast cells. We used a projection microscope and a computer analyzing system connected to a video scanner for the calculations. The mast cell count was higher in the irradiated groups than in the control group. The number of mast cells was higher in the groups irradiated with the shortest wavelengths (292 and 300 nm). In groups irradiated with wavelengths shorter than 307 nm a subepidermal clearance zone containing significantly fewer mast cells than the rest of the upper dermal layer was found. We suggest that the mast cells might have a digesting function, as this layer was cleared of elastotic fibers and few mast cells were seen here.