The study was carried out in the neritic and estuaxine waters of Porto Novo, Coromandel Coast, Bay of Bengal, India during the period January, t960 to December, 1967. The average displacement volume of plankton usually varied between 2 and 4 c~/mL During ssmmer, with a season of high plankton productivity, the average plankton displacement volume rose to 8 c~/m s. Generally speaking, the average zooplankton density (standing crop) was usually between 80,000 and 100,000 organisms/m s, of which copepods alone comprised usually between 70,000 and 90,000 organiaTns/m ~ The average copepod density per sample varied from 30,000 to 50,000 organisms/m a. t~owever, in the summer months, the copeped density was usually not less than 100,000 organisms/me; in some years this was even higher (from 125,000 to 170,000 orga~xisms/mS). Copepeds comprised between 80 and 95 % of the zooplankton population. The maximum non-copepod population in the zooplank~n seldom reached 30 %, was often below 25 %, and usually less than 20 %. During the period March to October (in some years as early as February, and in some years up to November), either an increasing or a steady trend of plankton production was evident. It would appear that salinity and rainfall determine the occurrence and distribution of plankton in Porto Novo.