A variety of agonists that stimulate inositol phospholipid turnover also activate phospholipase A2 (PLA2). This study examines the possibility that bombesin, a well-characterised calcium-mobilising peptide mitogen, may fulfil this criterion. The profile of arachidonic acid (AA) release, as well as the regulatory mechanism(s) behind bombesin-stimulated PLA2 activity, were examined. It was found that the AA released upon bombesin stimulation, was composed of two phases - an initial transient phase that is essentially independent of extracellular calcium and of PKC activation and a later, sustained phase that is absolutely dependent on extracellular calcium and shows a requirement for PKC activation. This study focusses on the first of these phases and the regulatory mechanism involved in release.