['There have been several case reports of improvement in the appearance of mature burn scars following treatment with fractional CO(2) lasers. However, the biochemical mechanisms responsible for these improvements have not been elucidated.', 'Ten patients with mature, full-thickness, hypertrophic burn scars received initial treatment with a fractional CO(2) laser. Clinical improvement was measured with Vancouver Scar Scale as well as Patient and Observer Scar Assessment Scale. Fresh tissue samples were obtained before the initial treatment and 48\u2009hours after the first treatment for TaqMan Real-time RT-PCR analyses. Expressions of several scar-related biological markers, including types I and III procollagen, matrix metalloproteinase (MMP)-1, -13, transforming growth factor (TGF)-β1, β2, β3, and basic fibroblast growth factor (bFGF), as well as microRNA miR-17-92 cluster, were investigated.', 'There were significant improvements in both observer and subject ratings in all scales. Both types I and III procollagen mRNA levels were dramatically down-regulated after treatment, but the ratio of types I/III procollagen mRNA was not different. The expression of MMP-1 was significantly up-regulated after treatment, while TGF-β2, -β3, and bFGF levels were significantly down-regulated. Expression of miR-18a and miR-19a were dramatically up-regulated (P\u2009<\u20090.05) after treatment.'] Do clinical and molecular effects on mature burn scars after treatment with a fractional CO ( 2 ) laser?