Gaps is a bedside diagnostic game. It is played in two versions by nephrologists. It deserves wider application by the practicing physician. The more popular version, Anion Gaps, shows the presence of undetermined anions and alerts the physician to the possibilities of laboratory error, severe derangements in serum protein metabolism, or the ingestion of certain ionic compounds that directly or indirectly alter the concentration of routinely undetermined anions. A second version, Osmolal Gaps, shows the presence of unmeasured osmoles or of increased plasma solids and can be used in a variety of clinical situations to direct attention to laboratory, error, hyperproteinemia, hyperlipidemia, or the presence of unmeasured osmoles in the serum.