By adding such substances as polytamine, a derivative of amino acids (a by-product of caseous fermentation of cow's milk), by-product of cow's milk caseous hydrolysis with acid, and ten different non-essential amino acids contained in polytamine directly to rabbit bonemarrow tissue culture, the author estimated the tissue growth area and cell density and studied influences of these substances on the production of the leucocyte series in the bone marrow. The results are as follows. 1. Both polytamine and by-product of cow's milk caseous hydrolysis with acid can increase the growth area slightly more than the control only in a high concentration. 2. With addition of L-hydroxyproline in the concentration from 0.1 to 0.0001 per cent, this substance in any concentration within this range increases the growth area and cell density 2-3 times that of the control, showing the greatest values among amino acids used in the present experiment. 3. Both L-proline and L-arginine in high concentration increase the growth area twice the control, and slightly at low concentration. 4. L-Cysteine, L-tyrodine, and DL-serine each in a proximal concentration can only increase the growth area slightly more than the control. 5. L-Aspartic acid and L-glutamic acid, glycine, and L-ornithine show hardly any significant difference as compared with the control.