Acatalasemia is the homozygote of an abnormal gene which is considered to be involved in the vital catalase synthesis of man, as discovered by Takahara in 1946. The hypocatalasemia which is a heterozygote of this abnormal gene, since its blood catalase activity is only about one half that of normal persons, has a characteristic of being accurately detected by the biochemical methods. In addition, it is of a great importance in the sense of gentics to determine its frequency by the cases of hypocatalasemia. As for the screening tests of this hypocatalasemia the titration with potassium permanganate has been mostly used, but the author devised a new method of determining catalase activities of the subjects by measuring the amount of oxygen gas produced from H(2)O(2) by the action of catalase, using the polarographic sensor. This method, compared with the available ones has a great advantage in that its accuracy, the ease of examinations and possible simultaneous screening tests with quantiative analysis are possible. Furthermore, this method is a superior one that it is easy to transport the test apparatus and conduct field examinations.