ECG measurements from 341 patients with inferior myocardial infarction (IMI) and 327 normal subjects were used to develop and test decision rules for the ECG diagnosis of IMI. Recursive partitioning provided a simple decision rule with 75% sensitivity and 97% specificity, using Q amplitude and Q duration in a VF, Q duration in III, and T-wave axis in the frontal plane as decision variables. Dropping T-wave axis from the decision rule led to a 10% decrease in sensitivity. Multiple logistic regression provided sensitivities and specificities which were similar to those for recursive partitioning. Both methods outperformed traditional noncontour criteria for IMI.