In a seminal paper, Robert E. Lucas, Jr. provided the theoretical relationship between aggregate demand and real output based on relative price confusion at the individual market level. Subsequently, an alternative New Keynesian aggregate supply relationship was derived and it was demonstrated that the two theories can be distinguished on the basis of how both the rate of inflation and the volatility of relative prices affect its slope. By emphasizing the first implication of New Keynesian theory, strong evidence was obtained supporting this model using international data. We also concentrate on the second difference between the two theories. We derive the individual market-level equilibrium relationship for the Lucas model, i.e., the disaggregate supply curve. We estimate the crucial parameters of the relationship between aggregate nominal demand shocks and real output using U.S. intranational state and industry data. We find that the Lucas model omits important New Keynesian features of the data.