The electrocardiogram of 100 normal subjects and 216 patients with arterial hypertension in different stages have been analysed. P wave especially has been taken into consideration: it is often abnormal in the presence of left ventricular hypertrophy (LVI). The point-score system elaborated by Romhilt and Estes allows, if only QRS-T is considered, to diagnose LVI in 32 of the hypertensive patients (15%) and in 41 cases (19%) if the increase of P wave terminal forces is emphasized. Nevertheless this P wave characteristic does not appear more useful than others (axis less than or equal to 40 degrees; duration greater than or equal to 0.12 sec; presence of notch). The best results are achieved by considering the coexistence of two or more abnormalities of the P wave. Thus LVI is diagnosed in 52 (24%) of our cases, without false positive.