Base excess blood, cBase(B), was introduced in the late 1950s by Ole Siggaard-Andersen to quantify the non-respiratory component in acid-base imbalance. Schwarz and coworkers in Boston argued that cBase(B) was not independent of pCO2 in vivo. Siggaard-Andersen introduced later the modified base excess, cBase(ecf), which has also been called standard base excess. Twenty years ago, on the 5th Meeting of the IFCC Expert Panel on pH and Blood Gases in Copenhagen, I showed that AVL, Corning (now Bayer), Instrumentation Laboratory (IL) and Radiometer had quite different algorithms for calculating cBase(B). All four used at least pH, pCO2 and ctHb for the calculation, IL used in addition pO2. I simulated 81 acid-base disturbances and calculated cBase(B) from the different algorithms. The calculations showed different values between different instruments, in particular in metabolic alkalosis. I proposed that the Expert Panel should work towards better standardisation in the calculation of cBase(B). If we look at the algorithms in use today for calculating cBase(ecf), the algorithms are not so complicated as the algorithms for cBase(B) and they are more uniform for all the manufacturers. This standardisation has led to the increased and effective use of cBase(ecf) in the clinical work.