The visual pigments in the rods of 15 species of deep-sea fish were examined by microspectrophotometry. In 13 species a single visual pigment was found. The λmax of these pigments, which ranged from 475 nm to 488 nm, suggest they give the fish maximum sensitivity to the ambient light in the deep, blue ocean waters where they live. In two species two visual pigments were found in separate rods. Bathylagus bericoides had rhodopsins of λmax 466 nm and 500 nm and Malacocephalus laevis had two rhodopsins of λ max 478 nm and 485 nm. It is noted that the species with two visual pigments tend to be dark in colour and live in deeper, darker, water.