Noninvasive stress and pharmacologic tests with procainamide and propafenone were studied as methods to identify patients with Wolff-Parkinson-White syndrome (WPW) who would otherwise be judged at risk of sudden death on the basis of electrophysiologic criteria: the shortest RR interval during induced atrial fibrillation less than or equal to 250 ms or accessory pathway anterograde effective refractory period less than or equal to 250 ms. Sixty-five patients were studied. Twenty-four patients fulfilled the electrophysiologic risk criteria (group A) and 41 patients fulfilled none of these criteria (group B). Persistence of preexcitation during stress test showed a sensitivity of 96% and a specificity of 17% to identify group A patients; its positive predictive value was 40% and negative predictive value 88%. With both procainamide and propafenone tests persistence of preexcitation identified group A patients with a sensitivity of 96% and a specificity of 51%; their positive and negative predictive value were, respectively, 53 and 95%. Stress and pharmacologic tests have good sensitivity and negative predictive value, but low specificity and positive predictive value.