Unusual phospholipid effects may occur when their distribution in the membrane is altered or when uncontrolled metabolic reactions yield elevated concentrations of their short lived derivatives. Serine phospholipids are normally buried in the internal side of plasma membrane. Upon exposure to the extracellular environment they elicit a response from selected cell populations. The interaction between these phospholipids and neuroactive compounds in rat peritoneal mast cells may indicate that serine phospholipids have a role in the nervous system during development