A review of recent studies on the interaction of cationic dyes with mucopolysaccharides (MPS) is given and the possibilities and limitations of the use of these dyes for quantitative staining are discussed. It is concluded that under certain conditions the extent of binding is stoichiometric and can be considered as an approximate measure of the total MPS content of the tissue. Quantitative differentiation of the various MPS by the use of cationic dyes is not feasible at present. Approaches along the lines of microchemistry seem to be more promising. Preliminary results are presented using a method based on fractional elution of MPS after precipitation with cetylpyridinium chloride of the MPS mixture from proteolyzed tissue. Samples are prepared by cryostat sectioning or microdissection and digested with papain. The lower limit of the method is a few [mu]g MPS per fraction; morphologically, structures of 50 to several 100 [mu] apart can be analyzed separately.