While using a needle for suturing in a restricted operating space, surgeons change the direction of the needle holder by modifying needle grips. Such directional changes, however, have not been analyzed systematically. The "left-hand rule", similar to Fleming's rule in physics, is proposed as a guide in comprehending these changes. When the thumb is assumed to represent the direction of the holder in the standard grip, the long axis of the index finger represents that of a grip in which the needle is held obliquely [oblique (Ob) grip]. In the usual (tip-ward) Ob grip with ordinary suturing (advancing the needle by supination), the holder is shifted in the direction opposite to the fingertip (towards the arm) and, in that with reversed suturing (by pronation), towards it. The middle finger represents a grip in which the needle is held after rotation [rotated (Ro) grip]. In the usual (counter-clockwise) Ro grip, the holder is shifted in the direction opposite to the fingertip (towards the back of the hand) in both ordinary and reversed suturing.