Daily variations of coastal marine phytoplankton populations were studied over a 31-day period in the northeastern Mediterranean, Bay of Iskenderun. Sampling was conducted between 21 June and 22 July 2002. In addition to phytoplankton sampling, chlorophyll a and nutrient analysis, seawater temperature and salinity measurements were done. Surface water temperature fluctuated between 25.2-30 degrees C. Salinities were generally low and ranged from 35.4 parts per thousand to 36.1 parts per thousand. A total of 120 phytoplankton taxa were detected during the study. Diatoms were the dominant group in terms of numerical abundance while dinoflagellates were dominant in terms of species diversity. Phytoplankton abundance varied between 10.8 x 10(2) and 112.2 x 10(2) cells l(-1). Temperature was one of the most important factor influencing the variations of phytoplankton and a positive significant correlation was found between temperature and phytoplankton abundance. Phytoplankton abundance and physico-chemical data showed fluctuations in this selected period. For this reason, it can be said that daily sampling provide important information on coastal phytoplankton succession and on the effects of related environmental parameters.