Soybean is the most important protein source in animal nutrition and is widely used in poultry diets. Several factors influence the concentration of amino acids present in soybean grains cultivated in Brazil, such as climatic changes, genetics, topography, and soil fertility. Many technologies of soybean processing are used in order to eliminate or inactivate both heat-labile and heat-stable anti-nutritional factors. During processing, soybean by-products with different nutritional values are also produced. Processing conditions may as well affect the coefficients of digestibility of nutrients that are present in soybean protein sources. Furthermore, positive and negative effects of the environment may be masked by changes in processing conditions. This study aimed to compare the levels of crude protein and essential and non-essential amino acids in soybean samples collected in the states of Goiás, Mato Grosso, Mato Grosso do Sul, Minas Gerais, Paraná, Rio Grande do Sul, and Santa Catarina during the harvest of 2003/2004 in Brazil. Measurements were made using NIRS (Near Infrared System of Reflectance Spectroscopy), and expressed on an "as-fed" basis. Soybeans sampled in different states evidenced nutritional differences. It is worth noting that samples collected in Minas Gerais, Rio Grande do Sul and Mato Grosso do Sul presented high levels of essential amino acids. The analyzed levels of essential amino acids were not always directly related to the protein concentrations of the samples. Because of the diversity of growing conditions in Brazil and worldwide, soybean produced in different environmental conditions is expected to show variable protein composition and quality, as demonstrated in the present study.