Techniques for quantitative evaluation of the growth of granulocytes were improved by staining the cells for their chloroacetate esterase and peroxidase activity. Neutrophil granules stained bright red and eosinophil granules, marked yellow. Limited growth of megakaryocytes was observed in bone marrow cultures. 2-Fluorohistidine showed marked suppressive action on the growth of granulocytes in cultures. Motion picture studies revealed a very interesting phenomenon of the so-called "novel cells." These cells changed into fast-moving cells and released from the culture surfaces a few hours after cultivation. They exhibited constant rapid protraction and retraction of projections of various forms, ranging from cytoplasmic filaments to wing-like membranes. The number of cells declined progressively, and the cells disappeared from cultures in a period of 3 to 6 days. Very long forms, often accompanied with various branches, of Mycobacterium lepraemurium were observed in macrophage cultures maintained at a lower temperature (30 degree). Studies of a combination of two antiamebic drugs, broxyquinoline and broxaldine in murine leprosy revealed little suppressive activity. BIBLIOGRAPHICAL REFERENCE: Nossal, R.J., and Chang, Y.T.: A procedure for determining mobility parameters for cells moving along surfaces. J. Mechanochem. Cell Motility 3: 247-251, 1976.