Hormones and neurotransmitters are released from cells by being passed through a fusion pore that forms following the fusion of the vesicle and the plasma membrane. The fusion pore can be a rate limiting step since it can either expand fully leading to the release of the entire vesicle content (full fusion exocytosis), or reversibly closes retaining vesicle integrity and some of the residual cargo ("kiss-and-run" exocytosis). By measuring changes in membrane capacitance, which is proportional with the membrane surface area, we can directly monitor fusion and fission events of secretory vesicles. We therefore used the cell-attached patch-clamp technique to directly monitor discrete changes in membrane capacitance in isolated rat lactotrophs at spontaneous conditions and after stimulation with cAMP-raising agents. Our results confirm that discrete changes in membrane capacitance very likely represent fusion/fission of prolactin-containing secretory vesicles with the plasma membrane. Furthermore, transient fusion events ("kiss-and-run" exocytosis) appear to be the predominant mode of exocytosis in rat lactotrophs at spontaneous and stimulated conditions. Finally, stimulation increased the frequency of these events events, whereas the frequency of full fusion exocytotic events was not affected by the cAMP-enhancing agents.