Quantitative determinations of the acid/base’excretion in urine are valuable in clinical cases where disturbances of the acidbase metabolism are found. The renal mechanism of regulating the acid-(base equilibrium is dealt with in text books of physiology. It shall only be recalled that an excess of hydrogen ions from nonvolatile acids has to be excreted in the urine. Here it is buffered either by a buff& system already present, mainly phosphates, in the form of “titratable acid”’(Henderson & Palmer, 1914), or by ammonia, produced by the kidneys. Similarly, an excess of hydroxyl ions will be excreted either in the form of ‘Ititratable base”, or buffered by the carbon, dioxide, always present, as bicarbonate ion. Thus the acidlbase excretion in urine can be expressed by the equation (Gamble, Ross & Tissdall, 1923): Net acid exwetion 2=