Some hypertensive and non-hypertensive subjects have a striking blood pressure response to a medical environment (white coat phenomenon), although it is unlikely that its presence, degree, and duration can be routinely predicted. Despite the common observation that "anxious" patients may present with this reaction when a physician measures their blood pressure, no psychological variables have thus far been linked to white coat phenomenon in formal analyses. Ambulatory blood pressure monitoring is a useful tool to disclose the phenomenon since it allows precise evaluation of repeated blood pressure measurements outside the medical environment. To investigate the possible relationship between psychological profile and white coat phenomenon, we have planned to administer a series of psychometric tests to 120 subjects undergoing ambulatory blood pressure monitoring. The present data are derived from an analysis of the first set of 70 patients. Thirty-four subjects who presented with white coat phenomenon (defined as office blood pressure elevated by at least 15% over the mean 24-hour ambulatory blood pressure value) and 36 comparable subjects who did not have this reaction underwent a series of psychometric tests evaluating cognitive behavior, hostility, cynicism, anger, anxiety state, coping ability and strategies, and quality of life. Of the various psychometric tests, the scores of three relevant scales (healthcare-related fears, mental efficiency and behavioral disengagement) were significantly higher in the group of patients with white coat phenomenon, while in both groups, emotional instability was higher than the clinical cut-off point. There were no significant differences between the two groups regarding signs and repression of anger (anger-out and anger-in), cynicism, hostility, or anxiety state. Our data seem to indicate that the subjects most likely to show an overt blood pressure increase in the medical environment are those who evidence healthcare-related fears and emotional instability but are not necessarily anxious. They exhibit high coping skills in cognitive resolution of stressing situations (such as blood pressure measurement) but do not combine these strategies with an adequate behavioral response and do not feel that behavioral involvement is necessary for the management of their clinical condition.