The method for the colorimetric determination of exchangeable calcium in soils, based on the reaction with glyoxal is proposed. The interference of some ions which are normaly found in soil extracts, (magnesium, copper, manganese, aluminum, iron and sulfate) as well as its elimination with KCN and trietanolamine, were studied. The new method was compared with the one using EDTA titration, the results showing the same precision for both.