Hairless (SKH-1) mice were mated with Beige (C57B/bb) mice to produce a hairless mouse deficient in neutrophil elastase (hhbb). These mice were exposed to 0.09J UVB irradiation for 5 months to see if neutrophil elastase was an important factor in elastin remodeling and development of solar elastoses. Analysis of peritoneal neutrophils confirmed that the hhbb mouse was deficient in elastase, retaining only 10% as much activity as the normal littermates (hhHb). Skin MPO activity was equally elevated in all the mice receiving UVB suggesting an equal influx of inflammatory cells. The absolute breaking strength of the skin in both the hhBb and hhbb mice was not altered by UVB treatment over the 5 month exposure period. Elastin quantitated biochemically as desmosine, or visualized histologically, was increased following UVB exposure in the normal mice. In the elastase deficient mice, however, the elastin fibers appeared to be unaffected by exposure to UVB irradiation at this level. The results suggest that neutrophil elastase is an important mediator in the development of solar elastosis resulting from continued exposure to UVB irradiation.