Distinction between benign and malignant pleural effusions is often a very difficult problem. Glycosaminoglycans play an important role in cellular proliferation and differentiation. The authors examined glycosaminoglycans in 17 samples, 11 malignant and 7 benign. Separation of glycosaminoglycans has been achieved by centrifugation-addition of trichloracetic acid-centrifugation-addition of cold ethanol. Glycosaminoglycans have been analyzed by electrophoresis on cellulose acetate sheets. 6 malignant samples had higher levels of HA and CS than standard. The authors distinguished benign effusions in two subgroups: inflammatory and cardiac. Among inflammatory, 3 had higher levels of HS and 1 of HA and CS. Further investigations are necessary to elucidate possible different patterns.