This paper provides a formal test of the null hypothesis of a unit root in the log-level of labor productivity against the alternative of linear trend stationarity with a one-time structural break in the level and slope of the trend at an a priori unknown date. Using some newly developed time series tests, we show that the log-level of productivity is more accurately modeled as following a deterministic trend with a regime shift rather than as a unit root process. Some implications of the results for detrending and for testing cointegration relationships between productivity and other variables are discussed. (JEL C22. O40)