In a 42-yr-old beech forest stand, growing on acid brown earth, five trees were felled every 2 wk. From their lowest trunk segments, each 100 cm in length, tracheal sap was collected by water displacement. The investigation was performed from mid-October 1988 to mid-October 1989, comprising a total of 130 sample trees. Xylem sap concentrations of calcium, magnesium, potassium, and manganese of 26 sampling series were analysed by atomic absorption spectrophotometry, and the pH values of fresh sap samples were determined. The seasonal variation in xylem sap concentrations of Ca, Mg and Mn in the lowest trunk sections showed a strong increase in the second half of March and in April, a decrease in May, after the leaves had expanded, a low level in summer, and a new increase in late autumn and winter. Potassium showed a different pattern with maximal xylem sap concentrations in autumn. Additionally, at four sampling dates (mid-March, beginning of May, mid-August and mid-November), four trees, one at each date were cut into sections for the determination of the mineral concentrations in the xylem sap along the stem.