Calcimycin (A-23187) is an antibiotic isolated from Streptomyces chartreusensis. It inhibits the growth of Gram-positive bacteria and some fungi. Calcimycin is a unique divalent cation ionophore (like calcium and magnesium) and can induce Ca2+-dependent cell death by increasing intracellular calcium concentration. The pyrrole polyether antibiotic calcimycin (A23187) is a rare ionophore that is specific for divalent cations. It is widely used as a biochemical and pharmacological tool because of its multiple, unique biological effects.