The family of EF-hand type Ca2+-binding proteins includes calbindin, S-100 alpha and beta, calgranulins, B and C, and the parvalbumin family members, including parvalbumin alpha and parvalbumin beta. The S-100 protein is involved in the regulation of cellular processes such as cell cycle progression and differentiation. S-100 protein may function in the activation of Ca2+ induced Ca2+ release, inhibition of microtubule assembly and inhibition of protein kinase C mediated phosphorylation. Two S-100 subunits, sharing 60% sequence identity, have been described as S-100 alpha chain and S-100 beta chain. Three S-100 dimeric forms have been characterized, differing in their subunit composition of two alpha chains, two beta chains or one alpha and one beta chain. S-100 localizes to the cytoplasm and nuclei of astrocytes, Schwann s cells, ependymomas and astrogliomas. S-100 is also detected in almost all benign naevi, malignant melanocytic tumours and in Langerhans cells in the skin. Calbindin, S-100 proteins and parvalbumin proteins are each expressed in neural tissues. In addition, S-100 alpha and beta are present in a variety of other tissues and calbindin is present in intestine and kidney.