The distribution and abundance of large marine debris were investigated on the continental slope and bathyal plain of the northwestern Mediterranean Sea during 3 oceanographic cruises undertaken in June 1994, July 1995 and April 1996. Different types of debris were enumerated, particularly pieces of plastic, plastic and glass bottles, metallic objects, glass and diverse materials including fishing gear. The results showed considerable geographical variation, with concentrations ranging from 0 to 78 pieces of debris ha(-1). In most stations sampled, plastic bags accounted for a very high percentage (more than 70%) of total debris. In the Gulf of Lions, only small amounts of debris were collected on the continental shelf. Most of the debris was found in canyons descending from the continental slope and in the bathyal plain, with high amounts occurring to a depth of more than 500 m. An additional cruise was undertaken using the manned submersible Cyana (provided by IFREMER). Sixteen dives (46.07 km distance on the floor) conducted in canyons off Marseilles and Nice (France) ranging from 40 to 1448 m in depth, enabled us to locate accumulation areas. All these results are interpreted in terms of hydrological conditions.