I investigate in this paper partial equilibrium labor supply responses to unemployment insurance (UI) in the US. I use administrative data on the universe of unemployment spells in five states from 1976 to 1984, and non-parametrically identify the effect of both benefit level and potential duration in the regression kink (RK) design using kinks in the schedule of UI benefits. I provide many tests for the robustness of the RK design, and demonstrate its validity to overcome the traditional issue of endogeneity in UI benefit variations on US data. I also show how one can use the weighted difference between the behavioral response to an increase in potential duration and to an increase in benefit level to identify the pure moral hazard effect of UI. I then use these estimates to calibrate the welfare effects of an increase in UI benefit level and in UI potential duration.