Most governments keep balance of payments statistics on exports and imports, by value, andconstruct international prices indexes in order to deflate these statistics. How can intrafirm trade(IFT), trade between related parties such as multinational enterprises (MNEs), bias theconstruction of these international price indexes? Economists have known for many years thatthe prices set by MNEs for intrafirm transfers -- transfer prices --- are normally not the prices that would be negotiated between arm's length parties (Diewert 1985, Eden 1985, Horst 1971).Does transfer pricing bias the export and import price indexes in any predictable fashion? Iffirms manipulate transfer prices to avoid taxes or tariffs, what is the appropriate transfer price touse in constructing export and import price indexes, in theory and in practice? These issues are important because related party trade is huge, representing half of US imports and one-third of US exports, and perhaps a third of worldwide merchandise trade flows.