The Sandoz Pressure System (SPS) is a widely used device for ambulatory blood pressure recording. The accuracy of blood pressure profiles recorded in daily routine with this device has been demonstrated. In 34 untreated hypertensive patients the blood pressure values were in good agreement with measurements taken by auscultation. The variability of recordings was less or equal to 5 mmHg in 10% of patients for the systolic and in 94% of patients for the diastolic value. During daily activity 100 +/- 6% (mean +/- standard deviation) of the values expected by programming were available for analysis. These results confirm that arterial pressure under ambulatory conditions cannot be reliably predicted based on blood pressure measurements in the doctor's office.