Abundance and distribution of unicellular cyanobacteria Synechococcus spp were studied during July 2001. Samples were collected from four different depths covering above the thermocline. Nitrate concentrations ranged from 0,005 mug at-l(-1) off Trabzon and Hopa to 1.284 mug at-l(-1) off Giresun. The highest concentration of Synechococcus spp. was at off Giresun at 25 m (6000 coil ml(-1)) and off Rize (3700 cell ml(-1)) at surface. Cyanobacteria cell counts were low at 5 and 10 m depths. The picoplanktonic abundance varies with nutrients in the Black Sea and it is quite lower in July 2001 somewhat similar to those observed in the oligotrophic Atlantic waters.