One of the basic cellular functions of nearly every cell type is the exocytotic release of synthesized molecules, stored and packaged into intracellular vesicles or granules. A variety of approaches has been used to identify and characterize the molecules that mediate vesicular trafficking along the secretory pathway. The findings obtained with these approaches suggest that common mechanisms may underlie a wide variety of vesicle-mediated transport steps. This review presents some of the recent findings regarding the study of the cellular mechanisms which control neurotransmitter and hormone release from neurons and endocrine cells respectively, and focuses on regulation of these mechanisms. The similarities between these two cell types can be seen as evidence to support the hypothesis according to which the regulated exocytosis apparatus could have evolved from a constitutive fusion machinery to which some key modulators have been added. Insight into secretory vesicles will be relevant not only to the understanding of vesicular trafficking or cell polarity but also to the understanding of higher nervous functions resulting from synaptic plasticity.