  We still do not have a "standard" model for the mass distribution of spiral
galaxies. I review various methods used to delimit the range of values of the
mass-to-light ratio of the disk, such as spiral structure criteria, the
influence of bars, warped and flaring HI layers, velocity dispersions, and
features in the rotation curve occuring just beyond the optical radius. It is
not yet clear whether disks are maximal or not.
