The exercise electrocardiogram of the patients with left ventricular hypertrophy was studied, especially on its STT change. Seventy six patients with essential hypertension, who were under good control, were included for the study. They were 52 males and 24 females. Their ages ranged from 33 to 70 years (the average was 51.6±7.8 years of age). The patients were divided into four groups according to changes in ST segment and T wave on standard 12 lead ECG (Ⅲ, aVR were excluded): Group A consisted of 10 subjects, whose ECG showed so-called "Strain Pattern"; Group B included 22 subjects, showing ischemic depression less than 0.5 mm below the isoelectric line or low T wave (T/R≦1/20 and R≧10mm); Group C included 17 subjects, junctional depression was equal to or exceeded 1.0 mm; Group D included 27 subjects without marked STT change. Twenty healthy men (6 males and 14 females) were studied as control. They ranged in age from 20 to 62 (the average was 36.7 ± 14.1 years of age). As a rule, they were subjected to the Master's test (double two step). In the pre-exercise electrocardiogram of Group A, QRS voltage, LAD and QT ratio were significantly greater than any other groups. In the post-exercise electrocardiogram, Group A showed chiefly T wave changes without ST deviation. I could not find any cases in the group with positive responce. Therefore, the "Strain Pattern" with marked QRS high voltage might be secondary STT changes. On the other hand, patients in Group B and D showed mainly ST changes and most of them were determined to have positive responce of the test. So, the STT changes without marked QRS high voltage might be primary changes.