To investigate the seed population of red-tide causative organisms, community structure of flagellates and dynamics of resting cysts were monitored monthly from May 1997 to June 1998 at five stations in Kamak Bay, where red-tide occurs year by year in summer in Korean waters. A total of 58 flagellate species were identified including 56 spp. Of dinoflagellate and 2 spp. of raphidophycean. Genus Protoperidinium occupied 25.0% of total species number and the highest at station 1 located in most inner bay. Standing crops of dinoflagellate were a maximum of 193,642 cells L-1 in June 1998. Dominant species comprised Prorocentrum dentatum in June 1997, and Prorocentrum minimum and Ceratium furca from May to June 1998. Raphidophycean appeared in a few stations when water temperature increased from May to June 1998. Resting cysts comprised 31 dinoflagellate cysts, representing 13 genera, 27 species, 4 unidentified, and 1 Chattonella cyst of raphidophycean. The abundance of resting cysts varied extensively by month: total cysts ranging from 457 to 1,048 cysts cm-3, living cysts from 144 to 564 cysts cm-3 and empty cysts from 313 to 662 cysts cm-3. Living cysts constituted 25.0-55.9% of total abundance and their ratio increased in winter. The abundance of the living cysts showed the significant relationships to water temperature (r2=0.44) as well as to the seasonal succession of planktonic cells in the water column. Only a few livinig Chattonella cysts were found from July to August and from January to February, whereas empty cysts appeared in March and April. Of dinoflagellate cysts 17 heterotrophic species were included, comprising 54.8% of total species number and showing higher abundance of 50.4-54.6% in inshore than that of 29.0-36.0% in offshore. This means composition ratio of heterotrophic cysts might be closely related to polluting degree in such frequently red-tide occuring area.