In order to use most effectively the Tully-Fisher relation as a distance indicator, we need to understand better the general properties of disk galaxies. Over the years, we have accumulated a large archive of multiwavelength imaging and spectroscopic data and we are currently using the entire set to probe the nature of spiral galaxies and to look for additional parameters that might affect the use of the TF relation for distance measures.

• Karen Masters used the 2MASS database to explore the effects of internal extinction in galaxies via statistical tests. She explored a simple photometric model for extinction which is able to qualitatively reproduce the observed trends and also revisited the issue of the variation in the amount of extinction with galaxy luminosity.

• Barbara Catinella has used a homogenous sample of some 2000 spiral galaxies to construct average, or template, rotation curves in separate luminosity classes, spanning 6 magnitudes in I-band luminosity. These template rotation curves show no evidence of velocity decline within the spatial scales over which they are sampled, even in the case of the most luminous systems. In contrast to some previous expectations, the fastest rotators (most luminous galaxies) have, on average, rotation curves that are flat or mildly rising beyond the optical radius, implying that the dark matter halo makes an important contribution to the kinematics also in these systems. The template rotation curves and the derived functional fits provide quantitative constraints for studies of the structure and evolution of disk galaxies, which aim at reproducing the internal kinematics properties of disks at the present cosmological epoch.

• Karen Masters and Chris Springob have combined the EGG HI and optical archival datasets to construct a new TF database, referred to as SFI++. This work is to be submitted for publication soon!