Immunofluorescent staining of mammalian cells has provided a reliable approach for detection of specific antigen expression in situ. An advantage of fluorescent markers has been their applicability to automated, high-throughput cellular analysis by flow cytometry. Flow cytometry has thus become an integral component of clinical laboratory diagnostics, particularly in the areas of immunology and hematology. One of the major drawbacks of traditional immunofluorescent staining, even with flow cytometric detection, has been the difficulty in detecting low abundance cellular antigens, some of which may have clinical and scientific significance. To address these problems, staining techniques have recently been developed to increase the sensitivity of cellular antigen detection by flow cytometry. In this review we will describe a few of these techniques and focus on enzymatic amplification staining as a means to generate a highly augmented antigen-specific signal. We will also discuss practical applications of enzymatic amplification for immunostaining of clinical specimens.