Differential diagnosis in disordered acid-base homeostasis is usually possible by measuring the pH, pCO2, pO2 and bicarbonate concentration, and enables differentiation between respiratory alkalosis and acidosis, and metabolic alkalosis and acidosis. Compensatory counter-regulation (respiratory or renal) can make correct assessment of the primary disorder problematic. Treatment of the underlying disease, in particular the provision of adequate oxygenation in respiratory disorders is of the essence. In chronic forms of metabolic acidosis, for example in chronic renal insufficiency and elderly patients, bicarbonate substitution should be initiated in order to prevent the negative effects on various organ systems. Sodium bicarbonate formulations that can be assimilated from the small bowel are especially tolerable and suitable.