The aim of this study was to elucidate further the precise nature of the so-called "white coat" (WC) effect. We enrolled 88 hypertensive (46 men, 42 women) and 18 normotensive (4 men, 14 women) subjects in whom beat-to-beat blood pressure (BP) and heart rate (HR) were measured with a Finapres device at rest (R period) and during conventional BP measurement (WC period). The WC effect was defined as WC period minus R period values of Finapres systolic BP. Using the same method, we also measured the BP and HR variations induced by mental stress (MS period) and by assuming the standing position (S period). Variability was estimated in the frequency domain for BP (BPV) and HR (HRV) and gave indices of the autonomic nervous system. Pulse wave velocity was taken as an index of arterial distensibility. In hypertensive subjects, the WC effect was significantly and positively correlated with the BP response to stress (0.51, P<.0001) and standing (0.63, P<.0001). An increased BPV was observed in the low-frequency band (0 to 0.150 Hz) during WC, MS, and S periods. In normotensive subjects, the WC effect was very slight and not correlated with the responses to stress and standing. In this group, the WC period was not accompanied with an increased BPV, unlike the stress and standing periods. HRV was similar in normotensives and in hypertensives: decreased, unchanged, and increased during MS, S, and WC periods, respectively. The PWV was significantly increased in the hypertensives relative to the normotensives, even in the quartile of those with the lowest BP (on average similar to that of the normotensives). This work shows that the WC effect is associated with an enhanced BP response to standing and mental stress; these three situations are characterized by an increased BPV in the low frequencies, suggesting a similar modification of the sympathovagal balance. The WC effect may entail an increased risk because it is associated with impaired arterial distensibility.