A thin-walled hollow cylinder is suspended by a fine torsion wire so that it penetrates a horizontal soap film stretched across the top of a cup. The cup is rotated at a steady speed. The film drags the cylinder around until further deflection is stopped by the torsion reaction of the wire. From the known dimensions of the cylinder and the torsion constant of the wire the drag is shown to be of the order of 0.04 dyne per cm. The measurement of the tangential drag of a soap film is suggested as an advanced undergraduate laboratory project.