OBJECTIVE: To investigate the influence of blood pressure variability on target organ involvement. METHODS: Using a cross-sectional study of a hypertension clinic at a district general hospital, 420 patients with newly diagnosed untreated essential hypertension referred on a consecutive basis from general practice and 146 normal subjects drawn at random from the Danish National Register underwent a variety of measurements which included: echocardiography with determination of left ventricular mass index and relative wall thickness and early morning urine albumin/creatinine ratio. Mean, standard deviation and coefficient of variation of automated clinic values; daytime, night-time and full 24-h period were extracted from 24-h ambulatory blood pressure (ABP) monitoring. 'White coat' effect and dip were calculated. Hypertensives were classified into subjects with high or low variability, into 'white coat' hypertensives or established hypertensives and into dippers or non-dippers. RESULTS: Standard deviation of daytime blood pressure (BP) was positively associated with target organ damage and BP level, which was not the case when variability was expressed as a coefficient of variation. Patients with high variability exhibited no more significant target organ damage than patients with low variability, but patients with established hypertension had significantly more target organ damage than the 'white coat' hypertensives. The 'white coat' effect as such was not associated with increased target organ involvement. Non-dippers had significantly more cardiac target organ damage than dippers, but the difference disappeared after correction for different 24-h BP level. CONCLUSION: BP variability data obtained by non-invasive ABP monitoring does not seem to improve the information inherent in the BP level.