The effect of intergalactic magnetic fields on the peripherical shape of a spiral galaxy is discussed. It is shown that a magnetic field contained in the galactic plane produces an elliptical shape in the outer regions, the most external isophote being more eccentric than the inner ones. It is difficult to identify this shape in real galaxies, but the effect of the intergalactic magnetic field cannot be ignored when the peripheries of galaxies are studied, and could be involved to interpret unexplained features observed in some spirals.
