For the purpose to clarify whether minimal catalatic activity exists in Japanese acatalasemic cells or not and the manner how extrinsic hydrogen peroxide affects the acatalasemic cells, the author performed tissue cultures using the skin specimens from four acatalasemic persons affected with Takahara's disease and studied the nature of these cultured cells. The results are summarized as follows. 1. Between normal and acatalasemic cultured cells, no morphological differences could be seen and the growth rate of these cell-lines was similar to one another. 2. On the activity of succinoxidase and cytochrome oxidase there could be observed no difference between normal and acatalasemic cells. 3. In each acatalasemic cell line the minimal catalatic activity was observed and it seemed that this activity has an important role in decomposing hydrogen peroxide under normal metabolic pathway. 4. After treating with 10-4M hydrogen peroxide, respiratory enzyme activities and the growth rate in the acatalasemic cells were markedly disturbed, while in normal cells these remained almost intact. 5. There could be observed no differences between normal and acatalasemic cultured cells after X-ray irradiation (200 to 600 r) on the succinoxidase activity, catalatic activity and growth rate.