This study examined the effect of stimulus conditions on rate pressure product (RPP) during ECT. Seizure duration as well as baseline, ictal, and postictal RPP were recorded in 28 patients who received ECT under four stimulus conditions (unilateral threshold, unilateral suprathreshold, bilateral threshold, and bilateral suprathreshold). Seizure duration did not differ between the stimulus conditions. RPP significantly rose from baseline under every stimulus condition. Both ictal and postictal RPP values were different between stimulus conditions (one-way repeated-measure analysis of variance). Pair-wise comparisons showed that unilateral threshold ECT produced significantly lower RPP than unilateral suprathreshold and bilateral suprathreshold ECT conditions. The selective differences in RPP during ECT as well as their correspondence with the known therapeutic potency of ECT under these stimulus conditions suggest that RPP may be a potential index of ECT's therapeutic potency.