K-562 is described as a pluripotent leukemic cell line which expresses a diversity of hematopoietic cell differentiation antigens. With the use of monoclonal antibodies (MoAb), we show that the expression of these antigens is either "modulated", i.e. they are not expressed in early logarithmic growth but are expressed in late logarithmic growth, or "continuous", i.e. they are not affected by proliferation and phase of culture growth. Whether an antigen is modulated or continuously expressed appears to be an inherent property of the subline, since the expression of myeloid antigen binding the MoAb, PM81, was modulated on cells from a clone, whereas, the expression of this antigen was continuous by the parent subline and an independent subline F-1. Continuously expressed antigens appear to be an integral component of the K-562 cell surface matrix, while modulated antigen expression appears to be influenced by culture growth conditions.