Treaties and other international acts series. 2261. Economic cooperation with British/United States zone, Free Territory of Trieste, under Public law 472, 80th Congress, as amended, agreement between United States and British/United States zone, Free Territory of Trieste, amending agreement of Oct. 15, 1948, as amended, effected by exchange of letters signed Trieste Mar. 29 and Apr. 19, 1951; entered into force Apr. 19, 1951.