(1) Vectorcardiograms of ventricular premature beats were taken from100 cases of normal and of various cardiac patients by the Frank lead system. In order to include also ventricular premature beats occurring only occasionally, they were first recorded by a tape recorder.(2) Vectorcardiograms of ventricular premature beats were classified into 3 main types according to the loop configuration and its direction. Type A resembled more or less left bundle branch block. Type B resembled also left bundle branch block in configuration of the vector loop, but its direction was different, the QRS loop being oriented to the right posteriorly. Type C resembled right ventricular hypertrophy with a conduction delay. Types A and C were divided into a few subgroups.(3) The T vector loop was usually oriented opposite to the maximum QRS vector in Types A and B and the terminal QRS portion in Type C. In the shape and the direction of inscription of the T loop, no specific tendency was found, except for a tendency that the secondary T vector loop was observed in occasional ventricular premature beats in normal cases to be inscribed most often in the same direction of the QRS loop.(4) Type A1 was more often found in cases of good conditions and Types B and C were found in cases of relatively poor conditions. Type A2 fell between.(5) Among the cases 35 cases had ventricular premature beats occurring only occasionally. No difference could be found from those occurring frequently in their vectorcardiographic configuration and clinical significances.