1. Proteoglycans (PGs) of the extracellular matrix (ECM) play an important role in several morphogenetic and differentiation events that occur during embryonic development. 2. The purpose of this work was to characterize the ECM PGs present during development of Drosophila melanogaster, in an attempt to elucidate their functional relevance. 3. The major 35SO4 incorporation into PGs occurred during the first instar larvae. Sulfated PGs (90%) from both first and second instar larvae were degraded by HNO2 treatment. 4. This result indicated that heparan sulfate proteoglycans (HSPG) are present in Drosophila ECM throughout early development. 5. Charge fractionation of PGs on DEAE-Sephacel columns indicated that most of them eluted at 0.45 M NaCl and were sensitive to HNO2. 6. The administration of beta-D-xyloside, a drug that competes with core proteins for the glycosaminoglycan synthetic apparatus, generated biochemical modifications in the ECM PGs together with alterations in larval locomotor behavior.