1. Blood samples were obtained simultaneously from femoral artery and vein, pulmonary artery and antecubital vein at rest and during isometric and dynamic exercise in six patients during cardiac catheterization and plasma noradrenaline was measured radioenzymatically.
2. Analysis of variance indicated that differences between vascular sites were not significant, whereas differences between patients (P < 0·001) and differences between activities (P < 0·001) were significant.
3. Mean systemic arterial concentrations tended to be lower than pulmonary arterial concentrations during each activity, although the difference was not significant.
4. We conclude that forearm venous plasma noradrenaline concentrations are representative of those from other sites.