This paper contributes to the discussion on the functioning of the monetary policy transmission mechanism in Japan during the past three decades. It extends the methodology of time-varying parameter vector autoregressions (TVP-VAR) by employing an identification scheme based on sign restrictions. This approach allows for an explicit account of the zero lower bound on the nominal interest rate. Results suggest differences in the transmission mechanism between the quantitative easing policy period and the periods when the call rate played the role of a monetary policy instrument. Monetary policy operating through call rate movements is found to influence output more than when it targets banksf balances held at the central bank. Monetary policy operating through quantitative easing is found to influence inflation, in sharp contrast to the previous literature.