The scrapie isoform of the prion protein, PrP(Sc), is the only identified component of the infectious prion, an agent causing neurodegenerative diseases such as Creutzfeldt-Jakob disease and bovine spongiform encephalopathy. Following proteolysis, PrP(Sc) is trimmed to a fragment designated PrP 27-30. Both PrP(Sc) and PrP 27-30 molecules tend to aggregate and precipitate as amyloid rods when membranes from prion-infected brain are extracted with detergents. Although prion rods were also shown to contain lipids and sugar polymers, no physiological role has yet been attributed to these molecules. In this work, we show that prion infectivity can be reconstituted by combining Me(2)SO-solubilized PrP 27-30, which at best contained low prion infectivity, with nonprotein components of prion rods (heavy fraction after deproteination, originating from a scrapie-infected hamster brain), which did not present any infectivity. Whereas heparanase digestion of the heavy fraction after deproteination (originating from a scrapie-infected hamster brain), before its combination with solubilized PrP 27-30, considerably reduced the reconstitution of infectivity, preliminary results suggest that infectivity can be greatly increased by combining nonaggregated protease-resistant PrP with heparan sulfate, a known component of amyloid plaques in the brain. We submit that whereas PrP 27-30 is probably the obligatory template for the conversion of PrP(C) to PrP(Sc), sulfated sugar polymers may play an important role in the pathogenesis of prion diseases.