As a part of the Bay of Bengal Process Study, several biological characteristics were investigated during summer monsoon (SuM; July-August 2001), fall inter monsoon (FIM, September-August 2002), spring inter monsoon (SpIM; April-May 2003) and northeast monsoon (NEM, Dec 2005-January 2006). Chl a carbon during SuM, FIM, SpIM and NEM averaged 688, 767, 1212 and 1057 mg C m sup(-2) in the western Bay 9WB) 518, 904, 789 and 1023 mg C m sup(-2) in the central Bay. Primary productivity (PP) averaged 326, 281, 366 and 280 mg C m sup(-2) d sup(-1) in the WB and 144, 306, 241 and 375 mg C m sup(-2) d sup(-1) in the CB respectively. Shallow euphotic depths (approx., less than 55m) apparently are not conducive for (PP) in the 0-120 m column. Heterotrophic bacterial carbon biomass was sizable and averaged 282, 662, 95 and 288 mg C m sup(-2) in the WB and was 677, 227, 104 and 333 mg C m sup(-2) in the CB during SuM, FIM, SpIM and NEM respectively. They appear very crucial in governing the abundances of microheterotrophs in the southern and, open-ocean regions of the Bay. Microzooplankton were much poorer in abundance than those in the Arabian Sea except during SpIM. Their maximum carbon biomass (WB: 233; CB: 327 mg C m sup(-2) in the top 120 m was observed during SpIM. In the upper 200 m, the mesozooplankton biomass did not show much variation between the season (WB: 222, 906, 2428 and 988 mg C m sup (-2) and CB: 587, 1036, 821 and 808 mg C m sup(-2) d sup(-1) respectively during SuM, FIM, SpIM and NEM). Incidentally it was mostly decoupled with chl a and PP. Cold-core eddies observed during most sampled seasons seem to bear an enhancing influence on the overall biological productivity processes