A transition from a moving striation to a helical oscillation was observed in the positive column of a helium discharge at a pressure of 0.4 mm Hg as an applied longitudinal magnetic field was increased. The frequency and amplitude of the moving striation decreased with increasing magnetic field. When the magnetic field reached a critical value of about 1650 G, a helical oscillation appeared and the two waves were observed to coexist. The striation disappeared with a further increase of the field, but the helical oscillation continued to exist.