Pfiesteriaand Pfiesteria-like organisms were reported to be linked to major fish kills(involving well over a billion fish) in North Carolina and Maryland estuaries on the U.S. east coast during the 1990s. Occurrences of these species have been recently reported from Korean waters including Chinhae Bay and the coast of Yeosu. In this study, the life cycle of Cryptoperidiniopsis brodyi and Pfiesteria piscicida were examined using DAPI staining. Their excystment and growth were stimulated directly by the addition of prey cells such as Rhodiminas salina. Amoeboid stages in C. brodyi and P. piscicida were never observed in culture, even after addition of filter-sterile fish mucus and tissue. The dominant life cycle stages consisted of motile flagellated zoospores and cysts. A typical dinoflagellate life cycle was demonstrated by direct observation and DAPI staining.