Inositol monophosphatase, commonly referred to as IMPase, is an enzyme of the phosphodiesterase family of enzymes. It is involved in the phosphophatidylinositol [PI] signaling pathway, which affects a wide array of cell functions, including but not limited to, cell growth, apoptosis, secretion, and information processing. Inhibition of inositol monophosphatase may be key in the action of lithium in treating bipolar disorder, specifically manic depression.