In the first part of this dissertation we invetigate if a reduction in standard hours can improve the employment level, generating the effect known as work-sharing. The innovation of our theoretical framework is to include adjustment costs of work force in the analysis. This feature introduces dynamic aspects, allowing us to evaluate firms behavior both in the short - run and long- run. Our conclusion is that work-sharing does not occur. In the second part of the dissertation we analyze the adjustment of labor input to changes in demand conditions. We use Brazilian data to estimate parameters such as the cost of adjustment relatively to the cost of being out of long-run equilibrium, and the speed of convergence, to both employment and hours. Our findings should be taken carefully, because of possible aggregative problems. We obtain evidences indicating that hours are costly to adjust in Brazil, compared to international standards.