Purified mucopolysaccharides and basophilic substances in human rib cartilage of different ages from complexes with cetylpyridinium chloride (CPC). The complex formation was tested via treatment with basic dyes. An almost complete blocking of Alcian blue stainability was seen after an 18-hour incubation in CPC. Shorter incubation times result in incomplete blocking. Temperature and concentration of CPC have no influence. Staining by Alcian blue is too slow, while staining after CPC treatment is too fast in relation to normal staining. Toluidine blue and acridine orange, in contrast, produce an intensive staining after 3–5 min in control sections, while after CPC treatment only the nuclei show stainability. Recoloration goes slower than with Alcian blue and is not yet fully completed after 18 h. Pure mucopolysaccharides on filter paper are completely stained by Alcian blue after 1 h. In CPC-treated samples some coloration is seen after more than 1 min staining with Alcian blue; with toluidine blue, it can already be seen after 10 sec to 1 min. Untreated sections need a considerably shorter time for reaching their complete staining intensity.