Abstract Molecular modeling of glycosaminoglycans, hyaluronan, chondroitin, chondroitin-4-sulfate, chondroitin-6-sulfate and keratan sulfate is presented. Semiempirical quantum mechanical calculations, PM3 method, have been used to locate the minimal energy regions in the conformational space around the β 1→3 and β 1→4 glycosidic linkages. The global minima obtained for each of the glycosaminoglycans correspond to a compact conformation across the β 1→3 linkage and to the standard extended form across the β 1→4 linkage. The higher minima obtained around the β 1→3 linkage reproduces the crystallographic data for hyaluronan. A complex of hyaluronan and hydrated chromium ion has been modeled as well (ZINDO method). The complexation at the β 1→3 linkage resulted in an extended conformation.