Mesopelagic fish were collected from a cruise with the R.V. “Dr. Fridtjof Nansen” to the northern Red Sea and the interior Gulf of Aden off the Republic of Djibouti in March 1981. Off the Republic of Djibouti five species of mesopelagic fishes were caught and in the Red Sea six species. Benthosema pterotum (Alcock) were dominant in both areas. In the Red Sea Maurolicus muelleri (Gmelin) were also abundant. The mesopelagic fish caught in the Red Sea showed a pattern of vertical migration similar to that observed in other areas, in spite of the special hydrographical regime. The number of gill rakers of B. pterotum caught in the Red Sea differed significantly from that of all other populations studied. The number of photophores of M. muelleri apparently do not differ much from other populations. B. pterotum from the Red Sea mature at a larger size than other populations, while M. muelleri mature at a smaller size. The relative fecundity of M. muelleri is higher in the Red Sea than in other regions studied, while no significant difference was observed in B. pterotum. Both species appear to be opportunistic feeders. Their feeding chronology in the Red Sea seems to be similar to those observed in other areas.