One of the difficulties in studying the role of chomosomal proteins in maintaining the structure and regulating the function of chromatin and chromosomes is the lack of specific biological assays for their detection and quantitation. This is particularly true for the nonhistone chromosomal (NHC) proteins which are frequently identified by mobilities in polyacrylamide gels. Since this group is composed of many proteins, some of which are posttranslationally modified, identification of a component by its mobility in gels is, at best, tenuous.