This review deals with cellular factors that contribute to individualities of vascular smooth-muscle function in different organ systems and at different levels of the vascular tree. Particular attention has been given to: membrane receptors responsive to catecholamines, serotonin, angiotensin II, dopamine, and acetylcholine; membrane properties, including resting and action potentials, and the Na+, K+ ATPase electrogenic pump; regulation of cellular Ca2+; contractile proteins; metabolism, and cell messengers. Differences in membrane receptors appear to be the major basis for the individualities found in various vascular smooth muscles. Differences in cell-membrane properties and Ca2+ regulation are also significant causes of variability. Cell metabolism and contractile proteins contribute relatively less to the individualities of vascular smooth muscle. Too little is known about cell messengers to assess their contribution to this individuality.