Blood pressure variability over a 24-hour period was compared between subjects with labile and those with established hypertension. For this purpose, a computer analysis of the blood pressure tracings, obtained with continuous unrestricted monitoring, was adopted, which characterizes the blood pressure variability in a quantitative manner. The following parameters were employed: the mean, the standard deviation, the coefficient of variation, the indexes of skewness and of kurtosis. No significant differences could be found between the two groups except for the mean value of the blood pressure. It is concluded, therefore, that the term 'labile hypertension' in inappropriate.