The Minnesota code was introduced in 1960, and since then, a number of computer programs have been written for classifying electrocardiograms according to the rules of the code. However, in 1982, extended rules for serial comparison based on the Minnesota code were published. This article presents the details of implementation of automated serial electrocardiographic comparison using the code. Its application in the West of Scotland Coronary Prevention Study, which was a double-blind trial of lipid lowering in 6.595 men, is also discussed.