Seasonal changes in lipid, glycogen, protein (N .times. 6.25) and ash content of the meat of Macoma balthica (L.) from five sampling sites in the Gulf of Gdansk were studied from 1981 to 1984. Lipid and glycogen were stored mainly during spring and at the beginning of summer. The lipid content of up to 36% of the dry weight observed in populations from the Gulf of Gdansk are among the highest values reported for bivalve mollusks. Potential causes of this high value are discussed.