A theory of cell–volume response to abrupt or gradual changes in extracellular osmotic conditions is outlined. The coupled transport of water and impermeable and semipermeable solutes is considered. Semipermeable solutes, including relatively small lipophilic molecules, like glycerol or urea, are permitted to absorb to the membranes of internal organelle bodies, where they diffuse with a configuration–specific lateral diffusion coefficient. Impermeable solutes (such as salts) are excluded from internal organelles, resulting in a significant osmotically inactive cell–volume fraction. Cell–volume expansion or contraction in response to anisosmotic conditions is shown to depend strongly on the internal absorption behaviour of semipermeable solutes, as well as upon membrane permeation parameters. The results of the analysis lay the foundations for accurate determination of membrane permeability variables, of importance to a variety of cellular transport processes, including those involved in cell cryopreservation.