This monoclonal antibody is an excellent marker for human cells in xenographic model research. It reacts specifically with human cells. It is a part of a new panel of reagents, which recognizes subcellular organelles or compartments of human cells. These markers may be useful in identification of these organelles in cells, tissues, and biochemical preparations. Recombinant MAb rHNA/344 recognizes an antigen associated with the nuclei in human cells. It can be used to stain the nuclei in cell or tissue preparations and can be used as a nuclear marker in subcellular fractions. It produces a speckled pattern in normal and malignant cells and may be used to stain the nuclei of cells in fixed or frozen tissue sections. It can also be used with paraformaldehyde fixed frozen tissue or cell preparations.