There are very few studies of the indicators which measure the effects of irradiation, even though it is very important in assessing the mechanism of radiation injuries and evaluating the effect of chemical protection against radiation hazard. Previous studies used either in vivo survival or in vitro cell counts to measure radiation effects. The study describes the use of cell volume, intracellar DNA, and cell counts as indicators of the effects of irradiation on cells in tissue culture, and demonstrated the effects of AET (S2-Amino-ethylisothiuronium bromide) as chemical protection against radiation hazards as measured by these three indicators. The results are as follows: 1) Combined use of the three indicators demonstrated that the effect of radiation on L-strain cell in tissue culture resulted from extension of the cell's mitotic phase and inhibition of cell division. 2) A positive correlation in the indicators was found with high dose irradiation (800r) of cells in tissue culture, but there was no correlation noted at lower test doses (200r and 400r). This finding demonstrated that it is necessary to study irradiation effects using these indicators in combination, especially at low dose exposures. 3) The study demonstrated that AET inhibited growth of irradiated L-strain cells and furthermore promoted cell bivision in tissue culture, thus showing the capacity for AET to tissue cells against irradiation. 4) Use of cell growth indicators such as cell volume, intracellular DNA, and cell counts, in combination, seems superior to previous methods of cell studies related to irradiation effects.