Exposure to solar UV radiation (UVR) leads to changes in the extracellular matrix of the dermis, which is largely composed of collagen and elastin. Collagen and elastin proteins and their corresponding mRNA were assessed in dorsal skins of hairless mice exposed to 0.64 J/cm2 UVR (295-400 nm), 5 days per week, over a 12 week period. A 48% increase in skin-fold thickness was accompanied by increased elastic tissue deposition and more compressed collagen bundles as assessed histologically. Collagen I mRNA levels were similar to those in control skins at 1, 2, 3 and 6 weeks of UVR and less than control levels at 9 and 12 weeks. Collagen III mRNA levels were elevated after 1 week of UVR, remained elevated for a further 2 weeks and then returned to control levels at weeks 6, 9 and 12 when changes are occurring in collagen I transcripts. There was no evidence of corresponding changes in collagen I and III protein levels assessed using electrophoretic techniques. These results suggest that damage to the extracellular matrix, consequent on UVR, is associated with some pretranslational events. Elastin mRNA levels were unaffected by UVR, suggesting that elastic tissue hyperplasia is a posttranscriptional phenomenon.