This paper studies the links between the evolution of Spain's balance of payments and Spanish-American economic diplomacy along 1917 and 1918. The development of these relations may be useful to explain a great deal about the downturn in Spanish foreign commerce during the last year of WWI. After their entrance into the conflict, the United States toughened their commercial policies and made the Spaniards work hard to keep both their international trade and the freedom of their merchant marine. Contacts between the two countries dealt also with the repatriation of Spain's foreign debt and the use of its extraordinary profits to make loans to the Allied nations. The negotiations ended up in March and August, 1918 with the signing of two bilateral agreements, whose consequences can be followed using the monthly figures of trade between America and the Iberian Peninsula.