This study analyses the structure of the market of agricultural tractors in Brazil and measures the impacts of concentration from the acquisition of Valtra by AGCO, the two larger companies in the local market, on the market power index (Lerner index). In order to do this, a demand function for agricultural tractors including intervention variables (dummies of intercept and slope) was conducted so that its parameters were used in the index. For this purpose, the methodology of Cointegration Analyses with a Vector Error Correction Model (VECM) was used. The results indicate that the concentration was not reflected in significant changes in price elasticities. On the other hand, the Lerner index, which is high in level, increased considerably after the merger due to the market share gains of AGCO.