Summary 1. The derivation of non-respiratory hydrogen ion (nrH +) is presented. It is calculated from three input values—arterial hydrogen ion (H +), arterial carbon dioxide tension (P CO 2 ), and hematocrit of the blood—by using both the Hender- son-Hasselbalch and ‘standard bicarbonate’ equations. 2. Six diagrams are shown to depict the various profiles of nrH + against the traditional acid-base parameters—H +, P CO 2 , HCO 3 −, and CO 2 content. Its most practical feature resides in the numerical similarity of its range of normal limits (38–45 nano-equivalents/liter) to both arterial hydrogen ion concentration (H +) and arterial carbon dioxide tension (P CO 2 ). as well as its property of providing both direction and magnitude. 3. A ‘see-saw’ approach to the visualization of acid-base situations is also introduced. As the primary compensatory acid-base organs, lung (P CO 2 ) and kidney (nrH +) are placed equidistant at opposite ends of a lever, and H + ion concentration is used as the dynamic fulcrum. Abnormalities of acid-base can thus be visualized as a teetering of the see-saw beyond the normal range.