This volume deals with the relationships between toxins and one of the most fundamental processes in any living cell - the secretory cycle. The reader will find up-to-date information on secretion, generated by experts in this fast evolving field. In the last decade extensive molecular and cellular studies have exposed the molecular similarity among most known secretory systems. In this book secretion is discussed from its basic mode found in yeast up to its most sophisticated version in neurotransmitter release in nerve terminals. A comprehensive view on the mode of action of toxins which block secretion but also those which cause hyper-activation of exocytosis is provided. This book addresses the issue of toxin action by deciphering the molecular and cellular basis of exocytosis in various organisms and cellular contents.