Single cell analysis by flow cytometry is a powerful diagnostic modality that has been limited by poor resolving power. Molecules expressed on the cell surface in abundance (i.e., greater than 1000 molecules per cell) can be detected readily by conventional staining technologies; however, molecules expressed in lower concentrations cannot be easily observed. Because there are many molecules that are functionally significant at lower levels of expression, the capability to detect these molecules is important. Enzymatic amplification staining is a new flow cytometric amplification technology based on the enzymatically catalyzed deposition of reporter molecules. This technology allows for the detection of molecules expressed on the cell surface at low abundance. The authors have demonstrated that EAS can be used to resolve the expression of molecules that cannot be resolved with standard amplification procedures. It has been shown that this capability is valuable in the diagnostic evaluation of patient samples; moreover, it is likely that EAS can be profitably used in the analysis of both malignant and reactive blood cells from various patients.