The "Blackwell"s Basics in Medicine" series deals with fluids and electrolyte balance. Each title addresses one particular topic. This first title focuses on salt and water, with further titles on acid base and potassium. The series goes on to cover organ pathphysiology with titles on renal failure and heart failure using the Socratic method. The series follows a standard structure comprising brief questions (progressing from the simple to the more complex) followed by short answers. Case presentations teach the fundamentals of fluid and electrolyte balance, and illustrate the various topics presented. The approach is based on solid pathophysiological knowledge applied to basic medical principles, enabling the reader to interpret clinical data based on sound pathophysiological concepts, and thus provide better patient care.