The potential of using differences in log crude mortality rates, matched age for age, as a simple means of comparing two mortality studies is investigated. Graphical displays of such difference, plotted against age, are advocated and a method of curve fitting described. A number of application are presented, and the results of this approach compared with known results where available. The latest available mortality data on smoker & non-smoker U.K. assured lives are analysed by this simple approach.