Abstract.A seasonal sampling program of five stations off the Island of Rhodes (SE Aegean Sea) was carried out in 1983–1984. Temperature, salinity, Secchi disk transparency, P‐PO4, N‐NO3, N‐NO2, N‐NH3, Si‐SiO2, and chlawere measured and phytoplankton species recorded. Cell concentrations and chlavaried seasonally. with the highest values in summer (l.2 times 104‐1‐‐1total mean cells; 0.13 mgam‐3total mean chla) and the lowest in winter (2.3 times 103, 1‐‐1total mean cells; 0.06 mg.m‐‐total mean chla). A variation in cell abundance among stations was also noted. Quantitative relationships among the recorded taxa showed that diatoms and dinoflagellates were richer in species composition (88 and 58 total species, respectively) than coccolithophores (8 species) and other flagellates (8 species). Comparison of phytoplankton samples from different depths and stations by cluster analysis showed an irregularity or discontinuity in species associations. The SE Aegean Sea was characterized as oligotrophic on the basis of the estimated nutrient and phytopl