Seasonal and spatial variations in bacterial and picoplankton abundances and bacterial production (thymidine incorporation rates) were determined in the water column up to 150 m in several stations in the central and eastern Arabian Sea. Higher bacterial densities of about 1 x 10 sup(9) cells L sup(-1) were observed during the intermonsoon periods of September and April/May compared to the southwest monsoon period of July/August and the winter period of February/March. Although primary production was low during April/May, bacterial production was much higher during this period unlike July/August. It also showed an increase from the northern to the southern Arabian Sea, suggesting the presence of high amounts of dissolved organic carbon in this area. High picoplankton densities, ranging up to 45 x 10 sup(6) cells L sup(-1) were observed during February, particularly in the northern Arabian Sea. Rapid turnover of bacteria during the intermonsoon period of April/May suggests the predominance of a 'microbial loop' in the foodweb and a prevailing source of dissolved organic carbon in the oceanic waters.