Introduction: Differentiated thyroid carcinoma (DTC) frequently presents as solitary nodules, a clinical entity found in 4-7% of normal population. Cytological examination of a fine-needle aspirate (FNA) of the nodule is the initial diagnostic procedure. However, a correct diagnosis cannot be made in 20% of cases and a thyroidectomy should be performed. Despite of increasing knowledge on pathogenesis of DTC several controversies still exist concerning its diagnosis and management. Changes in the proportions of different types of glycosaminoglycans (GAGs) have been described in most tumors. Previous data from our laboratory have shown that chondroitin sulfate is significantly increased in tumors (10-100 times) when compared to the normal adjacent tissues. The purpose of the present work is to investigate if the GAG content can be useful to distinguish normal from tumoral thyroid tissues. Material and methods: Fragments from normal and neoplasic tissue were obtained from eight patients after thyroidectomy. GAGs were extracted after tissue proteolysis followed by precipitation with ethanol. The identification and structural analyses of the GAGs were performed by electrophoresis on propilenediamine acetate buffer (PDA) and degradation with specific enzymes (chondroitinases AC and ABC). Results: Contrarily to the expected, there were no differences in the total amounts of GAGs between normal (3.6 ± 1.9 mg/g dry tissue) and tumors (3.4 ± 2.8 mg/g dry tissue) tissues. Nevertheless, there was a change in the profile of the types of GAGs. Normal tissues (n=7) are composed of heparan sulfate (average, 23.3%; range, 13.2-46.2%), dermatan sulfate (average, 46.4%; range, 39.1-84.4%) and chondroitin sulfate (average, 30.3%; range, 14.7-63.4%). On the other hand, seven out eight tumor tissues present only heparan sulfate (average, 41.1%, range, 11.6-81.9%) and chondroitin sulfate (average, 58.9%; range, 18.1-88.4%) in their composition. Discussion: In this relatively small number of patients we were able to discriminate normal from thyroid tumors regarding the GAGs profile. The absence of dermatan sulfate and the higher expression of chondroitin sulfate could be involved in thyroid carcinogenesis. and a Further studies are still needed, but the present results could be useful for the diagnosis of that neoplasia, mainly when FNA is suspicious. Supported by: FAPESP and CNPq.