Lentigo maligna (LM) may represent a tumour arrested in an in situ phase, lacking the angiogenic capacity and underlying dermal neovascularization required for invasive growth. The acquisition of an angiogenic phenotype might be associated with the development of lentigo maligna melanoma (LMM). To investigate this thesis, sections of formalin-fixed, paraffin-embedded tissue from 15 LMMs, and 11 LM excision specimens were stained with the vascular endothelial marker Ulex europaeus agglutinin I. Dermal vessels were counted and vascular morphometry was performed. In specimens in which LMM was present, dermal vascularity was significantly increased in LM compared with normal skin. The most significant increases were found for dermal vascular density (39 per cent increase, P = 0.008) and for total vessel surface area (62 per cent increase, P = 0.005). However, when no LMM was present, the vascular density underlying LM (79 +/- 9 vessels/mm2) did not differ significantly from that of adjacent normal skin (67 +/- 6 vessels/mm2), although focal 'hot spots' of increased vascularity were present. We conclude that increased dermal vascularity is present beneath in situ LM and that this increased vascular density is closely associated with the presence of invasive LMM in the same specimen.