We sought to use antibodies against structural (tropoelastin fibrillin) and nonstructural (decay-accelerating factor [DAF], serum amyloid P -SAP- components of elastic fibers to characterize fiber structure in neonatal skin, normal adult skin and adult skin with solar elastosis from advanced photoaging. We found by immunohistochemistry and by western blotting that DAF, unlike SAP, is present on cutaneous elastic fibers in neonates and young children, suggesting that DAF may play an early, integral role in protecting elastic fibers from destruction by complement. The most superficial portion of oxytalan fibers stained with antibodies against fibrillin and DAF, while anti-tropoelastin stained only the deeper portion of oxytalan fibers. This suggests that deep oxytalan fibers are composed of both elastin and microfibrils, while the most superficial component is composed solely of microfibrillar proteins. Solar elastosis showed increased fibrillin, DAF, tropoelastin and SAP. Thus, solar elastosis is composed of both microfibrillar and elastin proteins.