Available data on cell counts, chlorophyll concentration and plrotosynthetic uptake of'' carbon in the Mozambique Channel are reviewed; a few unpublished results from R/V ' Anton Braun' cruise No. 8 are also presented. Outside the Nosy-Be region (which has been extensively studied for some years), stations are widely scattered and particularly scarce during the southern summer. The main feature is the well-known contrast between productivity in neritic and in oceanic waters. The effects of hydrology and climatology on productivity, by means of several possibilities of nutrient enrichment, have not been studied yet; at Nosy-Be, the only place where the actual cycle was described, the initiating and the limiting factors of phytoplankton growth are still unexplained. The qualitative composition, as well as the quantitative importance of nannoplankton (less than 20/4 size) offer also an open field for investigations. In situ primary production per unit of chlorophyll in surface waters amount, as a rough average, to 6 or 7 mg carbon assimilated per hour and per mg chlorophyll a.