Book excerpt: The Fifth International Meeting on Cholinesterases convened in Madras, India, in September of 1994. The long and rich history and culture of India provided an excellent setting for the meeting. More than 120 delegates from Asia, Australia, Europe and North America heard 54 oral presentations and viewed 54 posters on current research on enzymes of the cholinesterase family. The aim of this book is to compile the presentations of the Fifth International Meeting on Cholinesterases into a volume that describes recent investigations on the structure and catalytic function of acetylcholinesterase (AChE), butyrylcholinesterase (BuChE) and related enzymes, as well as studies on the molecular and cellular biology of these enzymes and the genes which encode them. Cholinesterases enjoy a long and storied history in diverse areas. In basic biochemical research, AChE is one of the best studied, though yet enigmatic, of enzymes. The efficient catalytic function of this enzyme presents the biochemist with a fundamental challenge in understanding the relationship between structure and function. AChE and BuChE belong to a family of proteins, the alB hydrolase fold family, whose constituents evolutionarily diverged from a common ancestor. Proteins in this family have a wide range of physiological functions. In commerce, AChE is a prime target for agricultural insect control, and for the development of therapeutic agents for Alzheimer's disease.