  An attempt is made to set constraints on the otherwise ambiguous
decomposition of the rotation curves of low surface brightness galaxies into
contributions due to the various components of the galaxies. For this purpose
galaxies are selected which show clear spiral structure. Arguments of density
wave theory of galactic spiral arms are then used to estimate the masses of the
galactic disks. These estimates seem to indicate that the disks of low surface
brightness galaxies might be much more massive than currently thought. This
unexpected result contradicts stellar population synthesis models. This would
also mean that low surface brightness galaxies are not dominated by dark matter
in their inner parts.
