Blood pressure of 63 healthy male pilots and 20 primary hypertensive patients was measured with the "Smart LINK Ambulatory Monitoring System". The BP readings were taken every 30 min in daytime and 60 min at night for 24 h. The results showed that two peaks appeared at 7:00-9:00 A.M. and 16:00-19:00 P.M. and two valleys at 12:00-14:00 P.M. and 24:00-5:00 A.M. in healthy pilots, but the hypertensive subjects showed higher systolic or/and diastolic blood pressure continuously.