In the enzymic group of oxidoreducctases the key position occupies the enzymne catalase (1.11.1.6) which can not only reduce but also oxidize a molecule of hydrogen peroxide yielding molecular oxygen and water. The scope of this paper is to give an overview of the occurrence and the properties of the abundant enzyme catalase which is essential for all organisms with aerobic metabolism and defends living cell against toxic oxygen derivatives resulting in the metabolism. The enzymic properties of the three subgroups of the catalase family, ie. true catalases, catalase-peroxidases and non-heme catalases are discussed. The paper further concentrates on affinity-purified catalase A from the yeast Saccharomyces cerevvisiae the properties of which are compared with those found in the literature. The ex-periments presenting the stability and heme content of catalase A from the above yeast are reported. Observed data together with enzymic properties and structural features support the classification of yeast catalase A as a true - or typical catalase.