The vertical distribution of urea has been determined during a five year period ( from June 1976 to May 1981) at 21 different stations in the Baltic Sea on samples collected during 20 cruises. Results show pronounced seasonal variations with the highest concentrations (up to 1.86 uM) toward the end of the spring, while the lowest (down to 0.08 uM) were found during winter months. Except for some stations in the western Baltic Sea ( Arkona Basin, Hanö Bight and Bornholm Deep) the concentrations were notably higher above the halocline than below it. Areas around the Gulf of Finland and the Hanö Bight show elevated average concentrations while the lowest concentrations were found in the central part of the Baltic Sea. During the late spring and summer it may reach up to 80% of the nitrogen nutrient reserve on the higher levels of water.