The molecular defects in the catalase gene, levels of m-RNA and properties of the residual catalase studied by scientists are reviewed in human (Japanese, Swiss and Hungarian) and non-human (mouse and beagle dog) acatalasemia with reference to the bioinformatics. Japanese acatalasemia-I, the G to A transition at the fifth position of intron 4 of the catalase gene, limited the correct splicing of the mRNA and synthesized trace catalase with normal properties. Hungarian acatalasemia type C showed a splicing mutation. In the Japanese acatalasemia II and the type A and B of Hungarian acatalasemia, the deletion or insertion of nucleotides was observed in the coding regions, and the frame shift altered downstream amino acid sequences and formed truncated proteins. In the Hungarian acatalasemia D, the substitution of a nucleotide in the exon was found. In mouse and beagle dog acatalasemia, the substitution of nucleotides in the coding regions was also observed. Studies of residual catalase in Swiss, mouse and beagle dog acatalasemia showed that aberrant catalase protein degrades more quickly than normal catalase in cells. The experimental research in genetic toxicology concerning the effect of oxidative stressors (nitrogen monoxide, nitrogen dioxide and so on) on Japanese acatalasemic blood and acatalasemic mice is described. The clinical features of Japanese and Hungarian acatalasemic subjects are also described.