Unexplained syncope is a common medical problem. Intracardiac electrophysiologic studies (EPS) have been used to uncover the underlying arrhythmic mechanisms. Electrophysiologic studies are especially helpful in the management of patients with inducible tachyarrhythmias, but is of limited usefulness in those with normal EPS findings. We investigated whether clinical and noninvasive laboratory variables can predict the results of EPS in 89 patients with unexplained syncope. The prevalence of inducible ventricular tachycardia (VT) was 15%; supraventricular tachycardia, 15%; bradyarrhythmias, 41%; and normal EPS, 29%. We used multivariate discriminant function analysis to predict the results of EPS. The variables selected for identification of patients with inducible VT by this analysis include New York Heart Association (NYHA) functional class, gender, digitalis use, nonsustained VT, and atrial fibrillation. Based on our statistical model, performing EPS on 45% of the patients with unexplained syncope would result in a 90% sensitivity in detecting patients with inducible VT. The variables selected for identification of patients with normal EPS findings include: New York Heart Association functional class, heart disease, digitalis use, and intraventricular conduction. Based on this model, it would require that all but 12% of patients with unexplained syncope be studied to achieve a 90% predictive accuracy for identification of patients with normal EPS. During follow-up, recurrence rates for the different EPS categories did not differ significantly. The five-year cumulative survival among the EPS groups were as follows: VT, 37% +/- 28%; SVT, 90% +/- 9%; bradyarrhythmias, 71% +/- 10%; and normal EPS, 96% +/- 4%. Survival of the VT group differed significantly from that of the normal group. In patients with unexplained syncope, EPS findings can be predicted from clinical and noninvasive laboratory data. Mortality during follow-up relates to EPS findings.