In previous reports 1 and 2, the author experimentally verified te fundamental staining mechanism of fluorescent NTS dye by its deposits in various cells. In the present experiment an attempt has been made to see whether it is possible to perform supra-vital staining with this fluorescent NTS dye. At the same time observations have been carried out on the staining behaviors (or changes) induced by the accelerated permeability of cell membrane in the course of supra-vital staining with concurrent use of various surfactants (surface active substances), and the results are summarized as follows. 1, It has been found that flurorescent NTS dye, being an acidic dye, has affinity to denatured protein, revealing a staining mechanism similar to eosin, and it stains degenerated cells deeply. 2. It has also been elucidated that in the course of supra vital staining with acidic dyes such as fluorescent NTS dye and eosin, even when the medium pH is raised to 7.2, on the addition of such surfactants as Tween 80, saponin, osvan, linoleic acid, OX (an anti-tumor agent of unsaturated fatty acids from Xray-irradiated rabbit liver) the dye readily permeates the cell membrane and thus the entire cell is uniformly stained positively. 3. These surfactants accelerate the permeability of the dye through the cell membrane as their concentration is raised, but in the case with saponified solution of fatty acids such as linoleic acid and OX at a certain range of concentration they bind chemically with intracellular organellae, bringing about changes in protein electrical charge of the organellae and as the result the cell becomes no longer stainable. Therefore, this point needs to be taken into consideration when the supra-vital staining of cells is attempted with concurrent use of surfactants of fatty acid series. 4. With fluorescent NTS dye and eosin supra-vital staining has been tried on Ehrlich ascites tumor cells, liver cells, epithelial cells of intestine, and ascites cells. It has been demonstrated that there is at least some difference in the accelerative effect of surfactants on the permeability of cell membrane depending on the kind of the substances. The accelerating effect of osvan, which is cationic surfactant, is especially marked. In the case of Tween 80 (a non-ionic surfactant) its effect is weak. In the case of OX. it imparts a greater permeability to Ehrlich ascites tumor cells rather than to epithelial cells of intestine. From these results, it seems that to a certain extent the basis has been established for introducing selectively some of charged substances into tumor cells depending upon the use of these surfactants.