The plankton material was sampled in August 1997 from the Gulf of Gdansk. The Cyanobacterium Nodularia spumigena strain ( NSG 0897 ) was isolated from the samples. The effect of salinity on the growth of Nodularia spumigena was studied in the laboratory. Salinity had a significant effect on the number of cells, optical density, concentration of chlorophyll a , dry mass and growth rate. The Nodularia spumigena strain grew well in salinities 4-16 PSU. A salinity of 8 PSU is the best for the growth of this strain.