The commonly observed positive correlation between market concentration and profitability may be explained by noncompetitive pricing behavior, as argued by the structure-performance hypothesis, or by the greater efficiency of firms with dominant market shares, as argued by the efficient-structure hypothesis. By examining the price-concentration relationship instead of the profit-concentration relationship, this paper tests the structure-performance hypothesis in a manner that excludes the efficient-structure hypothesis as an alternative explanation of the results. The results strongly support the structure-performance hypothesis and are robust with respect to model specification, measurement of concentration, and econometric technique.