Identification of mouse bone marrow colony growth in agar-cultures by the nitroblue tetrazolium dye

Identification of mouse bone marrow colony growth in soft agar cultures has been realized by layering of the plates with nitroblue tetrazolium at the concentrations of 1 mg/ml. Granulocyte-macrophage colonies appear dark-blue coloured on the yellow surrounding medium and can be fixed, stored at 4 degrees C and counted few days later. This method allows the cultures to be assessed macroscopically and makes a better enumeration of small clusters even if spread and consisting of only 30-40 cells.