The sponge material from the Straits of Magellan collected by the research vessels "Cariboo" in 1991 and "Victor Hensen" in 1994, and by a shallow water diving team, were studied. Most of the investigated bottoms were soft or detritic and true rocky shores were seldom surveyed. However, alternative hard substrata are the holdfasts of dead laminarians, very abundant in the Straits, which represent a sort of microenvironment suitable for settling of sponges and other benthic organisms. Out of a total of more than 150 specimens, 44 demosponge species were identified. The resulting taxonomic pattern suggests a very heterogeneous sponge assemblage, partly related to the variety of the surveyed stations. Sponge communities are characterized by a patchy distribution, a high specific diversity and a low biomass. Most of the recorded species are of austral origin and distribution, confirming the Subantarctic character of the demosponge fauna of the Magellan Straits and its close affinity (14 species in common) with the fauna of the Antarctic continent. Twenty species identified in this study had never been recorded before from the Straits.