Information available on the chemical composition of marine species harvested from the Aegean sea is very limited. Proximate composition, in vitro enzymatic digestibility, total sterols. minerals, and fatty acids were determined for the most important finfish, crustaceans, and molluscs commonly marketed in Greece. Moisture and total lipid content varied with the species All finfish investigated were fairly high in protein ( (15-25 %) ) while the lipid content varied ( (0.2-) (17.1 %) ) depending on the season. Moisture and ash content varied within a narrow range. Protein quality was comparable to that of beef, chicken, egg, and pork, with few species being slightly inferior. Total sterols were high in eel ( (136 \mathrm{mg} / 100 \mathrm{~g}) ), gurnard ( (103 \mathrm{mg} / 100 \mathrm{~g}) ), lobster ( 159 (\mathrm{mg} / 100 \mathrm{~g})), shrimp ((108 / 100 \mathrm{~g})), mussel ((121 \mathrm{mg} / 100 \mathrm{~g})), and oyster ((150 \mathrm{mg} / 100 \mathrm{~g})). Mussels and oysters contain noncholesterol sterols which can reach about (40 %) of the total sterols. The mineral content was highly variable. The most abundant mineral in finfish was (\mathrm{K}) followed by (\mathrm{Ca}) and (\mathrm{Mg}) with lower levels of (\mathrm{Fe}, \mathrm{Zn}), and (\mathrm{Cu}). Similar trends were observed in crustaceans and molluscs. The remaining microelements were present in amounts below toxic levels. Five fatty acids (16:0, 16:1w7, 18:1w9, 20:5w 3, and (22: 6 \mathrm{w} 3) ) represented 55 to (90 %) of the fatly acid content. Palmitic acid ranged from 9 to (48 %) of the total fatty acids. Long chain (w-3) polyunsaturated fatty acids ranged from 5 to (49 %). Whiting contained almost (50 %) n-6 polyunsaturated fatty acids, ranging from 0.1 to (2.9 %). It is well established that biological differences do exist in most of the marine species which in turn can influence the values to be set for standards and composition. O 1995 Academic Press, Inc.