Vectorcardiograms with the Frank lead system were recorded in 122 healthy subjects (65 men, 57 women) and the effect of horizontal displacement of chest electrodes C, A and I on the vectorcardiogram was studied. The results obtained were as follows: 1) With electrode C displaced 2 cm to the right of the original position, Rz, Sz, and Tz increased, the azimuthal angle of QRSmax deviated backward and the QRS-T angle increased. Almost contrary changes were observed with displacement 2 cm to the left. 2) Rx, Tx, QRSmax and Tmax increased with simultaneous forward dislocation of electrodes A and I, but decreased with backward displacement of the electrodes. A greater influence on the direction of vectors was caused by shifting the electrodes backward. However, the elevation of QRSmax, the azimuthal angle of Tmax and spatial QRS-T angle changed slightly. 3) Changes greater than 1.0 mV and 10 % in one of the parameters (Rx, Rz, Sx, QRSmax, Tx, Tz, Tmax) were observed in 35-45 % of the subjects with a 2 cm horizontal displacement of electrode C, while an identical displacement of electrodes A and/or I caused the changes in more than 80 % of the subjects. 4) Therefore, in clinical use, it is acceptable to vary the position of electrode C horizontally within 1 cm from the original position in man and within 2 cm in women.