The bactrioplankton in the inshore zone of the Gulf of Gdansk in the vicinity of Gdynia, Orlowo and Sopot was investigated in 1991-1993.The numbers of colony-forming bacteria (CFU), the total bacteria number (TBN), their biomass (BBM) and bacterail production (BP) were determined.THe changes in TBN, BBM and activity of the bacterioplankton during their annual cycle corresponded to the growth dynamics of phytoplankton.