In a series of the bone-marrow tissue culture of the sternum and peripheral-leucocyte tissue culture of healthy persons, and the bonemarrow tissue culture of the femur and peripheralleucocyte tissue culture of young healthy rabbits, both by the cover-slip method, the author investigaed living conditions of monocytes and fixed and stained cultured tissues periodically. 1. Monocytes appear after 3 hours' culture, and their movement is most vigorous 9 hours after the start of culture, but from 24 hours on they begin to disintegrate gradually. 2. The movement pattern of monocytes is of D-type, showing the particular pseudopodial movement. 3. The wandering velocity of monocytes in bone marrow and peripheral blood throught the tissue culture shows no marked difference both in the case of man and rabbits, but in the later stage of culture the wandering velocity of the monocytes in peripheral blod becomes less than that of bone-marrow monocytes. 4. In the case where Giemsa stain is used for staining, for the fixation of cultured tissue a modified form of Zenker-alcohol-glacial acetic acid solution of my own devise is best, and next, Bouin's solution and Carnoy's solution are suitable. 5. As for the findings on the fixation and staining of monocytes, although they are a little inferior to those on the smear-stained specimens, they present the picture showing the actual movement pattern. 6. No differences can be found between bone-marrow monocytes and peripheral-blood monocytes both in man and rabbits by the vital observation and fixed and stained specimens in tissue culture. 7. No transformation either from monocytes to other cells or from other cells to monocytes can be recognized in the present experiment.