Immunophenotyping, as many other clinical assays, is interpreted only in the context of reference values obtained from healthy control individuals. While the use of these reference values, or ranges, has been commonplace in the clinical flow cytometry laboratory for well over a decade, there has been little consensus in standardizing how these values should be obtained, analyzed, or expressed. This report reviews the variables to be considered in establishing reference ranges and statistical methods which can be used. Additionally, examples are given of previously published reference ranges for a variety of specimens often submitted for immunophenotyping. © 1994 Wiley-Liss, Inc.