When cultured human vascular smooth muscle cells are exposed to sodium-free solutions oscillations in intracellular calcium concentration are observed. In some cells the oscillations are maintained at constant amplitude throughout the exposure to Na(+)-free solution, in others the amplitude of the oscillations falls to a lower, steady-state level. The oscillations are also activated and maintained in isotonic, Na(+)-free, K+ solutions suggesting that the underlying mechanism does not involve the opening and closing of voltage-dependent channels. The possible mechanisms responsible for this behaviour are discussed.