Medium pH determines the differentiation of human promyelocytic leukemia cells to basophils or eosinophils by culturing in a protein- and serum-free medium.

Cells containing large basophilic granules in the cytoplasm appeared after culturing human promyelocytic leukemia cells (HL-60) in a protein- and serum-free alkaline medium. These granules were stained with toluidine blue and alcian blue. Cells were morphologically and cytochemically similar to basophils. The existence of histamine in the cell lysates was detected in both uninduced and alkaline medium-induced HL-60 cells. After culturing HL-60 cells in a protein- and serum-free acidic medium, cells containing eosin-stained small granules (eosinophils) appeared. The differentiation of HL-60 cells to basophils or eosinophils may therefore depend on medium pH by culturing in a protein- and serum-free medium.