This paper analyses the Nairu in the euro area and the influence that monetary policy had on its development. Using the Kalman-filter technique we find that the Nairu has varied considerably since the early 1970s. The Kalman-filter technique is applied here for the first time using explicit exogenous variables. In particular, real interest rates were found to explain a quarter of the increase in the Nairu between 1980 and 1995. This indicates the possibility of a long-run nonsuperne utrality of monetary policy.