The seasonal changes in concentrations of calcium, iron, potassium, magnesium, manganese and sodium in above- and below-ground parts of eelgrass (Zostera marina L.) were studied at three locations in the Limfjord, Denmark.The concentrations of calcium, iron and manganese in eelgrass differed significantly at the three stations. Above-ground parts of eelgrass contained significantly higher concentrations of potassium and manganese than below-ground parts, whereas the concentrations of iron and sodium were highest in the below-ground parts. Calcium and mangnesium concentrations in the two fractions were not significantly different.Significant seasonal variations were observed in the concentrations of calcium, potassium, manganese and sodium in above-ground parts of eelgrass and in the concentrations of iron, magnesium and sodium in below-ground parts. Iron, potassium, manganese and, to an extent, sodium showed a similar seasonal pattern with maximum concentrations in the summer and minimum concentrations in the spring or fall, whereas calcium concentrations in the above-ground parts showed the opposite pattern.The observed seasonal variation patterns are discussed in relation to the respective metals and changes in environmental factors.