Sphygmomanometry is the most common technique of blood pressure (BP) determination. In order to study effects of predictability and controllability in sphygmomanometric BP measurements, 72 normotensive healthy subjects were examined. BP was determined continuously and non-invasively using a Finapres device (Penaz-technique) and by sphygmomanometry. Five sphygmomanometric measurements took place, during the fourth the arm cuff was inflated to 300 mmHg, the others were done with a pressure of 175 mmHg. Subjects were randomly assigned to one of three groups: In one group the recordings were unpredictable to the subject, in the second group measurements were announced 1 min before cuff inflation took place, and in the third group, subjects could decide when the sphygmomanometric recordings should occur. With unpredictable measurements systolic and diastolic BP decreased (approx. 5 mmHg). When sphygmomanometric recordings were controllable or predictable to the subject BP remained relatively stable. We would suggest that automatic BP devices (e.g. in ambulatory BP monitoring) should generally work with acoustic signals, making cuff inflation predictable for the subject.