The paper examines the effects of a multilateral reduction of customs duties on non-agricultural goods, under a “nonlinear Swiss formula,” on Poland’s foreign trade, including both exports and imports. As part of the Doha Development Round of the World Trade Organization (WTO), countries are trying to work out a mathematical formula according to which national customs tariffs would be reduced. This is the key focus of ongoing negotiations concerning Non-Agricultural Market Access (NAMA). The author analyzes the newest version of the Global Trade Analysis Project (GTAP), known as GTAP 6.0, according to four scenarios. The GTAP model is a multiregional, multi-sector model that is often used to study the effects of commercial policy. The author describes the results of the multilateral negotiations according to their state as of the end of August 2006. The scenarios analyzed by the author differ in terms of “reduction coefficient A” under the Swiss formula. However, in all variants, the coefficient for developed countries is lower than that for developing countries. The analysis shows that the reduction of customs duties will have a limited impact on Poland’s foreign trade. All scenarios point to a small increase in the volume of exports and an insignificant drop in the volume of imports, accompanied by a rise in import prices and a decline of export prices. The deterioration of the country’s terms of trade is the most visible in the most radical scenario. The European Union as a whole would be more visibly affected than Poland by the planned reduction of customs duties. Similarly, the move would lead to limited changes in the overall volume of industrial production in Poland, though, in terms of individual sectors, there will probably be a clear drop in the production of clothing, textiles and leather goods, accompanied by a small increase in output in the wood industry. Changes in the volume of trade, production and employment are the most visible in the radical scenario. In all options, the reduction of customs duties will have no perceptible influence on Poland’s gross domestic product, though GDP in purchasing power parity terms will decrease as a result of deteriorated terms of trade. There will be a marginal deterioration in the overall level of prosperity in Polish society. This will be due to the fact that the drop in terms of trade will outweigh the increase of consumer surplus.