This book, which originated in the presentations of a symposium sponsored by the Universidad Nacional Autonoma de Mexico, held in Mexico City on April 14-16, 1980, represents an attempt to analyze some of the most relevant aspects of synaptic transmission. This topic was chosen on the strong belief that the progress of the neurosciences depends to a great extent on the understanding of the basic mechanisms of synaptic function. Rather than selecting only a specific approach or speciality, the book intends to cover this field in a multi­ disciplinary way. This means that neurochemical, neurophysiological and morphological studies are mingled throughout the book, which hopefully will help the reader to integrate the different faces of the same problem. Across the book the presynaptic component of synaptic transmission and its regulation is stressed much more than the postsynaptic phenomena. Although this might be a limitation, it has the advantage of increasing the focus of the book on a series of events which are gaining importance and interest every day.