In this study, we examined autonomic influences on pulse transit time measured from the R-wave of the electrocardiogram (R-PTT). Six subjects received three doses each of isoproterenol and atropine. Isoproterenol produced a significant linear decrease in R-PTT, a significant linear increase in heart rate (HR), and a significant linear decrease in diastolic blood pressure (DBP). Atropine produced a significant linear decrease in R-PTT and significant linear increases in HR and DBP. The R-PTT shortening effect of isoproterenol may reflect positive inotropic effects of beta- sympathetic myocardial stimulation. The R-PTT shortening effect of atropine may reflect reduction of parasympathetic inhibition of ventricular myocardial activity. However, possible vascular contributions to these effects remain to be determined. Nonetheless, the results encourage further examination of R-PTT in research concerning autonomic regulation of cardiovascular activity.