We investigated the relation between morning blood pressure (BP) variations, sympathetic activity, and QT intervals in 156 never-treated subjects with essential hypertension and different patterns of morning BP increase. The morning BP peak (MP) was defined as a rise in systolic BP >or=50 mm Hg and/or diastolic BP >or=22 mm Hg during early morning (6:00 to 10:00 AM) compared with mean BP during the night. Clinical characteristics of patients with morning BP peak (MP+, n= 69, morning systolic BP=+54+/-4, diastolic BP=+32+/-5 mm Hg) did not differ from patients without BP peak (MP-, n= 87, morning systolic BP=+24+/-5, diastolic BP=+19+/-3 mm Hg). The daytime (10:00 AM to 10:00 PM) and the nighttime (10:00 PM to 6:00 AM) BP profile did not differ between the two groups. During daytime and nighttime ECG monitoring, the corrected QT (QTc) interval, and QTc dispersion did not differ significantly between the two groups, whereas during the morning period the QT values were significantly broader in the MP+ group compared with the MP- group (P<or=0.001). Morning LF/HF ratio was significantly higher in MP+ patients than in MP- patients (P<or=0.02). Both systolic and diastolic morning BP, in combination with ratio LF/HF power, were significant predictors of QTc dispersion (adjusted R(2)=0.59, P<or=0.01) and QTc interval (adjusted R(2)=0.41, P<or=0.01), whereas inclusion of physical activity and echocardiographic parameters did not add explanatory information. The prolongation of cardiac repolarization times and morning sympathetic overactivity coexist in hypertensive patients with morning BP peaks, and they might contribute to raised cardiovascular risk in these patients.