AIM: We studied the effects of mental stress on the tone of the radial artery, a medium-sized muscular artery. METHODS: Using an A-mode echo-tracking device coupled to a photoplethysmograph, we took continuous measurements of the radial artery diameter, heart rate and finger arterial pressure in six healthy young volunteers. RESULTS: Under mental stress, the heart rate increased from 63 +/- 4 to 74 +/- 4 beats/min (mean +/- SEM, P < 0.01) and systolic pressure from 123 +/- 5 to 140 +/- 6 mmHg (P < 0.05). No consistent modification in the arterial diameter was observed at this time. CONCLUSION: The activation of sympathetic nerve activity induced by mental stress does not cause a significant contraction in the radial artery.