ABSTRACT NEIL R. ERICSSON, DAVID F. HENDRY, AND KEVIN M. PRESTWICH The UK Demand for Broad Money Over Long Run Using data from Friedman and Schwartz (1982), Hendry and Ericsson (1991a) developed an annual model of the demand for broad money in the UK over the sample 1878 - 1975. We update that model through 1993 on data extended by Attfield, Demery and Duck (1995), taking account of changed data definitions. The concept of parameter constancy is discussed. Using appropriate measures of opportunity cost and credit deregulation, the model's parameters are empirically constant over the extended sample, which was economically rather turbulent. Models based on Friedman and Schwartz's phase-average data fare poorly, both on the original sample and on the extended dataset. Some policy implications are drawn.