  We propose a method of distance determination based on the internal structure
and dynamics of disk galaxies. The method relies on the universal luminosity
profile of a stellar disk represented by an exponential law. Calibrating nearby
galaxies with known distances, it is found that the scale length of the disk is
tightly correlated with the specific combination of central surface brightness
{\it and} rotational velocity at a characteristic radius of 2.15 scale lengths
from the center. This suggests that the scale length of the disk may be used as
an indicator for extragalactic distance scale. The application of this relation
to M51 and M100 allows us to arrive at the distances of about 6 Mpc and 14 Mpc,
respectively, implying a Hubble constant of $H_0 = 92 \sim 94$ km s$^{-1}$
Mpc$^{-1}$.
