The mechanisms of Ca2+ level regulation in the cytoplasm by neurotransmitters, hormones, and growth factors and described. The role of G-proteins, second messengers and protein kinases in the regulation of activity of Ca2+ channels and pumps is discussed. The contributions of the endoplasmic reticulum, plasma membrane, nucleus, mitochondria and other intercellular compartments to the increase in the cytoplasmic Ca2+ concentration are estimated. The data concerning the relationships between the activities of systems of active and passive Ca2+ transport across the membrane are reviewed. The general mechanisms of intracellular Ca2+ oscillation are summarized, and a possible role of this process in the neuroendocrine signal transduction is discussed.