In order to evaluate the diagnostic value of exercise-induced Q wave changes and its relationship with the extent of coronary involvement and presence and location of a previous myocardial infarction, we examined the stress electrocardiograms of 188 consecutive patients with chest pain. Coronary arteriography shoved single vessel disease (SV) in 28 patients and multivessel disease (MV) in 130 patients; a previous myocardial infarction was present in 64 patients. The Q wave amplitude was measured as average of ten values in CM5 at rest and at peak exercise; a Delta-Q less than 0, i.e. reduction or no change of Q wave at peak exercise, was considered a positive response for coronary artery disease. The Delta-Q criterion shoved a significantly better sensitivity than ST depression, as a whole, but this improvement was nullified when patients with anterior myocardial infarction were excluded; as well specificity of Delta-Q although better than ST, did not allow a significant improvement for the diagnostic value of stress test. We also evaluated the diagnostic accuracy for multivessel coronary artery disease of both criteria positive was 78% whereas the negative predictive value of both criteria negative was 91%. We concluded that the exercise-induced Delta-Q less than 0 is a good indicator of coronary artery disease, although not superior to ST depression; the negativity of both criteria seems to be highly reliable for the exclusion of multivessel coronary artery disease.