During the investigations carried out in 1990–1991 in sediments of the lake Drūkšiai 17 free amino acids were identified. The greatest amount of free amino acids was found in silt of deep-water sampling stations. The lowest amount of free amino acids was registrated in the zone of unloading canal. Neutral amino acids dominated, whereas amount of sulfur-containing and alkaline amino acids was low. A large amount of amino acids was in combinations. According to the quantity of irreplaceable amino acids the sediments of the lake Drūkščiai equate with sapropel. Constantly and in rather large quantities such amino acids as valine, threonine, serine, aspartic acid and dlutamic acid, which stimulate development of cyanobacteria, were found. In winter on the average 51 % of free amino acids decompose and from sediments pass into the water. Total amount of free amino acids in the fluid phase of sediments was 14 times larger then in epilimnion.
Keywords: lake sediments, free amino acids, lake Drūkšiai, Lithuania.