Maintenance of brain cell volume is of crucial importance for normal central nervous system (CNS) function. This review considers volume regulation primarily in response to disturbances of body fluid osmolality. Brain cells counter the tendency to swell or shrink by appropriate adjustment of their internal osmotic potential. This is achieved by loss or uptake of inorganic ions and low molecular weight organic solutes (osmolytes). The latter comprise mainly amino acids, myoinositol, choline, and methylamines. Taurine may be of particular importance in volume control, especially in young animals. Brain cell volume regulation, however, is only one contributory factor to maintenance of constant brain volume (water content), and operates in parallel with important alterations in bulk fluid and electrolyte movement across the blood-brain barrier and between the interstitium and cerebrospinal fluid, which themselves moderate the requirement for transient alteration in cell volume during acute osmotic imbalance. Although altered cerebral content of inorganic ions and osmolytes are usually regarded as responses, respectively, to acute and chronic osmotic disturbances, osmolytes (especially taurine) may also participate in short-term cell volume regulation.