In perfoming bone-marrow tissue culture of human and guinea pigs the author observed the influences of the temperature, the osmotic pressure and the hydrogen ion concentration of the media on magakaryocytes; and obtained the following results. 1. The range of temperature at which megakaryoctyes can move about is from 30°C the minimum to 41°C the maximum, and the optimal temperature is around 35° to 39°C. The fromation of tentacle-like processes can be observed at the optimal temperature and most suitable temperature is about 38°C. 2. On the whole the vaculole formation can be seen markedly at a relatively low temperature, while the formation of secretion granules tends to appeare more promptly at a higher temperature than than at a low temperature. 3. More megakaryocytes appear in the growth zone in a relatively hyposmotic pressure (ΔT=-0.43 to -0.45) than in isotonic, and also the acceleration of the cell motility can be recognized in the case of human bene marrow, but it seems to be due to a transient stimulation. On the other hand, in the hyperosmotic pressure hardly any formation of tentacle-like processes in megakaryocytes can be recongized. 4. Degenerative changes tend to appear promptly as the pressure fluctuates either way from the isotonic, and the higher the osmotic pressure the greater is this tendency. 5. The optimal pH of the medium for megakaryocytes is 7.63-7.92 in the case of human and 7.75-8.07 in the case of guinea pigs. 6. Of the media used separately such as physiological saline solution, serum, and Ringer's solution, for megakaryocytes Ringer's solution is most suitable followed by serum, but in the physiological saline solution the movement of megakaryocytes is completely inhibited,