The most massive components of the microplankton were studied in the open sea waters for the first time at the end of the autumn season. It has been found that abundance of the virio- and bacterioplankton exceeded that observed in winter in the coastal zone. Against the background of a relatively uniform distribution of bacteria, the viral abundance and the lysis-mediated bacterioplankton death rate reached the maximum values in the most cold and salty waters of the northern sea areas.