Anti-human Ki-67 antibodies. These single-color reagents are of value to the study of cell cycle and proliferation. The Ki-67 protein is expressed in all proliferating cells during late G₁, S, M and G₂ phases of the cell cycle while cells in the G₀ (non-cycling cells) phase consistently lack the Ki-67 antigen. Un-stimulated normal human cells do not express the Ki-67 antigen.