This paper gives a valuation formula for LDC debt which is used to assess: (1) the price at which a buy-back of the debt is advantageous to the country; (2) the value to the creditors of having the flows of payment guaranteed against the extrinsic stochastic disturbances faced by the country; and (3) the trade-off between growth of payments and levels of payments. We finally offer an assessment of the Mexican agreement reached early in 1990.