Regulated exocytosis is the process by which specialised secretory cells including neurons and endocrine cells specifically release their contents. This process occurs in response to a specific cellular signal, usually an increase in the intracellular calcium concentration. While an increase in the calcium concentration is widely considered as the activator of the process, protein phosphorylation can be considered as a mechanism to regulate or fine tune this process. Recent evidence has indicated that the serine/threonine kinase, Akt/PKB, may play an important role in this modulation of the exocytic response. Evidence for the role of Akt has come predominantly from studies in glucose sensing and insulin secreting cells, such as adipocytes and pancreatic cells. We have used of range or cellular and biochemistry approaches to determine whether the role of Akt in the modulation of exocytosis extends to neurotransmitter release at the synapse. Acute stimulation of neuroendocrine chromaffin cells with physiological secretogogues or depolarisation of cerebellar granule neurons (CGNs) resulted in increased expression of activated Akt (P-Akt), demonstrating a relationship between an exocytotic signal and Akt activation. The functional effect of Akt in the modulation of exocytosis was then considered in both chromaffin cells and CGNs, with expression of wild-type Akt in chromaffin cells resulting in a slowing of the catecholamine release kinetics. This effect was shown to be phosphorylation specific, as expression of kinase-dead Akt had no effect on kinetics. Having identified a functional role for Akt in the modulation of exocytosis, we endeavoured to identify the substrates that may mediate these effects. In vitro phosphorylation assays demonstrated that Akt strongly phosphorylates Cystine String Protein (CSP) on Ser10 and Rab3a Interacting Molecule (Rim1) on Ser413. Furthermore, co-expression of CSP with wild-type Akt in chromaffin cells results in increased Ser10 phosphorylation, which was not observed when CSP was co-expressed with a kinase-dead Akt. These findings indicate that CSP is a cellular Akt substrate that may in part be responsible for the modulation of release kinetics. Taken together, these findings indicate that Akt may be an important kinase in the modulation of exocytosis at the synapse and that these effects may be mediated through the phosphorylation of exocytic proteins including CSP and Rim1.