This paper uses data from machinery dealers to estimate the retirement and depreciation patterns for a broad set of conventional machine tools. According to the dealers, the average service life of these machines at the survey date was about thirty years. Service lives were even longer in the mid-1970s, with the reduction over time likely caused by the diffusion of superior, computer-controlled machines. Consistent with the relatively long average life, the conventional machines have depreciated slowly. The author uses the results to asses the average service life assumed by the Bureau of Economic Analysis to construct capital stocks for metalworking machinery. Copyright 1996 by Oxford University Press.