Sixteen fish aggregation devices (FADs) were deployed in 50 to 500 m deep of water in the Canary Islands. Species composition and abundance were determined by visual census carried out by divers on 55 occasions from April to October 1995 and from August 1996 to May 1997. A total of 15 species representing nine families of fish were observed. Pseudocaranx dentex (Bloch and Schneider, 1810), Seriola spp. and Naucrates ductor (Linnaeus, 1758) were the most abundant species. The number of species associated with FADs increased with immersion time, but fish biomass did not increase. The maximum number of fish species registered exactly under the FADs at any one time was five. The average estimated biomass was 9.47 Kg per FAD (SD= 25.2). However, when only baitfish were taken into account, the mean aggregated fish biomass was 3.20 Kg (SD= 4.32). The estimated biomass was higher when Coryphaena spp. was present, increasing to 53.9 Kg per FAD (SD=53.6). A significantly lower fish biomass and number of species was observed in FADs deployed in shallower waters (50-100 m depth).