This article reviews what is known about the volume regulatory responses of lymphocytes. We present a discussion of recent data and hypotheses pertaining to the underlying mechanisms in regulatory volume increase (RVI) and regulatory volume decrease (RVD). New results from our laboratory are included to demonstrate that RVD is modulated by both temperature and pH, and that RVD occurs in proliferating as well as quiescent lymphocytes. This information is considered in the context of a model that includes the dynamics of membrane potential, K+ conductance, Cl- conductance, a proposed stretch-activated conductance, gating mechanisms, and equilibrium potentials, as RVD progresses. The physiological relevance of volume homeostasis in lymphocyte function, in particular, and in cell growth and proliferation, in general, is discussed.