Experiments have been performed on leucocytes in peripheral blood of rabbit to study the effect of high hydrostatic pressure on their degenerative changes and collapse. The results are as follows: 1) Leucocyte number of all sorts decrease with the lapse of time. Especially pseudoeosinophilic leucocyte has this tendency remarkablly, but basophilic leucocyte undistinctly. 2) Under action of pressure, the more the pressure increases, the higher the tendency of decrease of leucocyte. The decrease per-centage of lymphocyte number are lower than that of pseudoeosinophilic leucocyte, but basophilic leucocyte lowest. 3) As the leucocyte forms are changed by strong compression (500-1500 atm. pressure), degeneration factors can not be proved. Some original methods appear to be neccessary to prove the effects of high pressure on leucocyte. 4) From these results man can suppose that the resistance of lymphocyte is stronger than that of pseudoeosinophilic leucocyte and that of basophilic leucocyte is stronger than that of eosinophilic leucocyte and monocyte. But it seems to be dangerous to decide the all tendency of last three sorts of leucocytes, because they are very few in whole number.