Placenta growth factor (PlGF) is a member of the vascular endothelial growth factor (VEGF) family, comprising at least five cytokines specifically involved in the regulation of vascular and/or lymphatic endothelium differentiation. Several lines of evidence indicate a role for PlGF in monocyte chemotaxis and in potentiating the activity of VEGF, but the exact function of this cytokine is not fully understood. To define the biological role of PlGF in vivo, we have produced a transgenic mouse model overexpressing this factor in the skin by using a keratin 14 promoter cassette. Our data indicate that PlGF has strong angiogenic properties in both fetal and adult life. PlGF overexpression results in a substantial increase in the number,branching and size of dermal blood vessels as well as in enhanced vascular permeability. Indeed, intradermally injected recombinant PlGF was able to induce vessel permeability in wild-type mice. The analysis of vascular endothelial growth factor receptor 1/flt-1 and vascular endothelial growth factor receptor 2/flk-1 indicates that the two receptors are induced in the skin endothelium of transgenic mice suggesting that both are involved in mediating the effect of overexpressed PlGF.