Radiation environment of the Danube river from Bratislava city (Czechoslovakia) down to the river mouth was investigated systematically within 1981 to 1985. This report summarizes the data obtained in CMEA member-countries who participated in this work: Czechoslovakia, Hungary, Roumania, Bulgaria and the USSR. The samples for radioactivity measurements were taken at 21 points over 1869 km distance. Mainly the samples of the river water and sediments have been studied with measuring total alpha- and beta-activity and identifying such nuclides as natural uranium, radium-226, potassium-40, tritium, strontium-90 and cesium-137. The measurements data are presented. In general the radiation environment of the Danube river is considered as favorable, it does not differ from the state observed in previous time periods. No contribution by Nuclear Power Plants to the Danube river radioactivity has been revealed. The evaluated dose commitments for critical groups of population are four orders of magnitude lower than those from the natural radiation sources. 20 tabs.