A mental arithmetic test (the stressor; 15 min) significantly increased systolic and diastolic blood pressure, heart rate and plasma adrenaline by 11%, 12%, 28% and 152% respectively, with a prompt return to resting values after the test. Plasma noradrenaline and serum cortisol did not increase significantly during the 15 min of stress. Afterwards, however, the concentrations of both hormones increased, resulting in a total and significant increase averaging 19% and 23%, respectively. Plasma adrenocorticotrophic hormone (ACTH) did not rise significantly, but it was only measured before and at the end of the stressor. As a measure of parasympathetic nervous function, the beat-to-beat variation of heart rate, expressed as the mean successive square difference (MSSD), was employed. Four to 14 months later, the investigation was repeated, and resting values of all measures were found to be stable. The increments in systolic blood pressure and heart rate were significantly lower at retest. MSSD at stress, but not at rest, was significantly lower at retest. The mental arithmetic stress test as described here produces a sufficient autonomic response to make it viable for laboratory stress research. However, if repeated examinations are desired, the lower response at retest should be taken into consideration.