This paper analyses the consequences of financial rationing on temporary and stationary equilibria. We suppose that central bank policy has direct influence on activity by controlling the nominal supply of credit. The hypothesis of imperfect (slow) price adjustment allows us to distinguish different macroeconomic regimes. We reinterpret the phenomenon of effective supply failures, developped by.Blinder [1987], as the result of the dynamic instability of the classical unemployment regime when the steady-state investment demand of producers is financially rationed.