Chemical analysis was performed on samples of horse mackerel (Trachurus trachurus L.) caught monthly off the Portuguese coast throughout a period of one year (May 1997–April 1998). In the period between August and January the amount of total lipids present was recorded showing a minimum in February. Protein content remained fairly constant during the whole one-year period. Seasonal variation of lipid classes was followed and fatty acid profiles of total, polar and non-polar lipids as well as that of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were determined. The non-polar lipids were the ever dominant group, mainly composed of triacylglycerols. Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were the main phospholipids mainly containing 20:5ω3 and 22:6ω3, but PE was richer in 22:6ω3.