1. Addition of nicotinamide (l0-2M) into the culture medium brings about an increase of the NAD content and the inhibition of the growth of L cells in culture. This rise of NAD brought about by nicotinamide lasts for 2 to 3 days,
and thereafter gradually subsiding, it returns to normal level. 2. When L cells are cultured for several days in the same medium without addition of nicotinamide, there occurs a slow-down of mitosis with lapse of cultivation time but it has been found that this is in no way connected with the intracellular content of NAD. 3. By the addition of isonicotinic acid hydrazide (l0-2M) into the culture medium, there can be recognized a decrease of NAD content in L cell and the inhibition of cell growth. 4. In the case when 3-acetylpyridine (l0-2M) is added, a decrease of intracellular
content of NAD in L cells and a marked inhibition of the cell growth can be observed. In the groups cultured in the media, containing 3-AP at the concentration of l0-3M or l0-4M can be seen neither inhibition nor acceleration of the cell growth. The oxygen uptake of the cells cultured in the medium containing 3-AP (l0-2M) hardly differs from that of the control group cultured in the medium not containing 3-AP. 5. On the basis of these results discussion has been made on the relation ship between mitosis and NAD content in the cell.</p
