Since 24-hour blood pressure monitoring seems to be superior to occasional blood pressure measurement as far as risk stratification is concerned, we compared the two methods in patients with secondary hypertension and left ventricular hypertrophy. In 26 haemodialysis patients (12, mole, mean age 54 +/- 13 years), the mean occasional blood pressure values during haemodialysis were 147 +/- 18/82 +/- 9 mmHg, the mean 24-hour blood pressure values were 145 +/- 21/ 85 +/- 13 mmHg, during the day 145 +/- 23/86 +/- 13, during the night 143 +/- 25/81 +/- 13 mmHg. The nocturnal reduction of mean blood pressure was -3.6 +/- 7%. Both methods of blood pressure monitoring showed a significant correlation with the relevant echocardiographic parameters of left ventricular hypertrophy, cardiac mass and interventricular septum diameter. Patients with and without a nocturnal reduction in blood pressure could not he differentiated by the mean occasional blood pressure values. Therefore, 24 h ambulatory blood pressure monitoring seems warranted in this high risk group, especially to monitor antihypertensive drug therapy.