Some experiments on C-14 uptake and cell numbers were made with the purpose of comparing nannoplankton and net phytoplankton from surface sea-water samples collected at six stations in Equatorial waters (Fig. 1). The results of these experiments showed a pronounced difference between nanno and net phytoplankton in photosynthesis and in cell numbers (Table I). The net phytoplankton represents an average of as little as 9.93% of total photosynthesis and 22.20% in numbers of organisms of total phytoplankton. The results obtained in coastal and in oceanic waters show that the effect of the proximity of land on standing stock and upon primary production is well marked (Table II). The results obtained are discussed and compared with data of earlier papers.