Fibulin-5 null mice display abnormalities in the elastic fibres in the dermis. We postulated, therefore, that fibulin-5 might be a regulator of elastic fibre assembly and stability. To clarify the role of fibulin-5 in elastic fibre formation, we employed in vitro systems that allowed increasing expression of elastic fibre components by gene transduction using retroviral vector constructs. First, the human tropoelastin gene (ELN) was transduced into human dermal fibroblasts, which resulted in elevated gene expression. These cells were then cultured in monolayer, but the overexpression of ELN in this system did not alter the assembly of elastic fibres. However, incubation of fibroblasts with TGF-beta1 resulted in elastic fibre accumulation, and the expression of fibulin-5 was enhanced by TGF-beta1. Thus, we overexpressed human fibulin-5 cDNA in dermal fibroblasts using a retroviral vector containing a cytomegalovirus (CMV) promoter. These cells deposited elastic fibres. These results suggest that fibulin-5 is a critical component in the control of elastic fibre assembly by dermal fibroblasts.