The purpose of this paper is to understand disequilibrium phenomena at a disaggregated level. By using data on French firms, we carry out the estimation of labor demand model with two regimes, which correspond to the Keynesian and classical hypotheses. The results enable us to characterize classical firms as being particularly good performers: they have more rapid growth, younger productive plant and higher productivity gains and profitability. Classical firms stand out, with respect to their production function, by higher growth rate of disembodied technical progress and, with respect to their accumulation behaviour, by more rapid investment and replacement rates which lead to the rejuvenation of their capital stock. But the production-employment elasticities and production-capital elasticities, as well as the accelerator, are identical for classical and Keynesian firms.