Suspended particulate matter (SPM) data from two surveys carried as part of the Canary Islands Azores Gibraltar Observations (CANIGO) project, in September 1997 and January 1998, are presented for the Gulf of Cadiz and the SW coast of Portugal. Analysis of total suspended mass, particulate organic to inorganic matter ratio, δ13C(PDB), and a microscopic analysis of particle composition were performed. Our objective was to quantify and characterise SPM in the water masses present in the study area, North Atlantic central water (NACW), North Atlantic deep water (NADW), and especially in the Mediterranean water (MW). MW was usually characterised by values of SPM higher than NADW but similar to NACW, and was different in terms of SPM composition: higher δ13C(PDB) values and relative abundance of mineral and biogenic particles, but lower relative abundance of particles <10 μm. The higher values of δ13C(PDB) and biogenic material in MW suggest the presence of “fresher” particulate material relative to the other water masses. In terms of SPM, two different MW can be described, a well-defined high-salinity and high-temperature slope MW, and an offshore MW in areas away from the continental slope and the seafloor. Slope MW showed higher particle abundance than offshore MW. It also showed a different particle composition, with higher values of δ13C(PDB), mineral particles, biogenic particles, and lower values of particles <10 μm than offshore MW. No significant difference in SPM composition was observed between the upper and lower cores of MW. Three SPM sources to MW are proposed: a MW origin source (Gibraltar Straits or Mediterranean Sea), bottom sediment resuspension, and surface waters. We suggest the occurrence of a constant particle source in surface waters near Gibraltar and/or in the Mediterranean Sea during both surveys. In the eastern Gulf of Cadiz, the input of sedimentary particle into slope MW was slight or non-existent. On the western Gulf of Cadiz and off the west coast of Portugal, both surface and sediment inputs appear to be important particle sources into slope MW.