The past two decades have witnessed several marine microbiological investigations being carried out by different workers on the east and west coasts of India. The enumeration of the heterotrophic bacteria of the surface and bottom waters, muds and plankton tows and of certain physiological groups had been carried out off the coast of Madras, in the Palk Bay and the Gulf of Mannar. The nature of the bacterial flora associated with sea water and fishes off Malabar Coast had also been worked out though less exhaustively. The quantitative as well as the generic distribution of bacteria in sea water off Cochin and in fresh fishes caught therein has recently been studied, Marine bacteria producing B12 and certain antibiotics had been isolated from the sea water and marine muds off Bombay Coast. Investigation on marine yeasts was first done in Bombay waters and subsequently studies were made in Vellar Estuary and the near-shore waters of Porto Novo. The distribution of yeasts in the Indian Ocean has been studied recently during the International Indian Ocean Expedition. The occurrence of marine bacteriophages had been reported earlier at Bombay and the recent International Indian Ocean Expedition has met with bacteriophages in the bottom and off East African Coast. Valuable information on the geographical distribution, movement and the biochemical activities of bacteria inhabiting the Indian Ocean has been provided by some of the earlier Soviet Oceanic Expeditions.