The present study was undertaken to determine if leads CM₅, CC₅, and V₅ are equally sensitive in detecting ST segment depression with exercise or hyperventilation in apparently normal males. Seven physically active men (29.4 + 2.9 yrs, 180.9 + 2.5 cm, 77.9 + 3.4 kg, x±SEM), free of risk factors for heart disease, were initially found to have J point (J₀) depression with mild exercise in lead V₅. Simultaneous ECG recordings from CM₅, CC₅ and V₅ during seated rest (REST), immediately post-moderate exercise (IPE), and after 30 s of hyperventilation (HVT). ECG signals were manually evaluated for ST segment depression at the J point and 60 ms and 80 ms past the J point (J₆₀, J₈₀). None of the three leads differed in their ability to detect ST segment changes. With exercise, J₀ was significantly (P<.05) reduced compared to REST; neither J₆₀ nor J₈₀ differed from REST. HVT reduced J₀ significantly but not J₆₀ or J₈₀ Exercise provoked greater reductions than HVT. These data suggest that, in apparently healthy adult males, these three ECG leads are equally able to detect J point changes with exercise and hyperventilation, but exercise results in a relatively greater downward ST segment shift than does hyperventilation.