Changing smooth muscle phenotype and abnormal cell proliferation are important features of vascular pathology, including the failure of saphenous vein bypass grafts. We have characterised and mapped protein expression in human saphenous vein medial smooth muscle, using two-dimensional (2-D) polyacrylamide gel electrophoresis. The 2-D system comprised a nonlinear immobilised pH 3-10 gradient in the first dimension (separating proteins with isoelectric point values between pH 3-10), and 12%T total gel concentration sodium dodecyl sulphate polyacrylamide gel electrophoresis in the second dimension (separating proteins in the range 14,000-200,000 Daltons). Using a combination of peptide mass fingerprinting by matrix-assisted laser desorption/ionisation-time of flight mass spectrometry and partial amino acid sequencing by nanospray tandem mass spectrometry, a subset of 149 protein spots was analysed, with 129 protein spots being identified and mapped. The data presented here are an important addition to the limited knowledge of venous medial smooth muscle protein expression in vivo. Our protein map will facilitate the identification of proteins differentially expressed in human saphenous vein bypass grafts. In turn, this may lead to the elucidation of molecular events involved in saphenous vein bypass graft failure. The map should also provide a basis for comparative studies of protein expression in vascular smooth muscle of varying origins.