Can rotation curves reveal the opacity of spiral galaxies ?

Long-slit optical spectra along the major axis of spiral galaxies constitute a main source of information concerning the kinematics of galaxies. In highly inclined spiral galaxies the long-slit spectrum is distorted by dust, which obscures the innermost parts of the galaxy and eliminates the relevant kinematic information. This effect however may provide information concerning the amount and the spatial distribution of dust. Here I review previous attempts to quantify the internal extinction of spiral galaxies using kinematic information and I discuss the relevant theoretical models. Finally I suggest possible directions for further studies on this subject.