  I derive a general expression for the optical depth $\tau$ for gravitational
lensing of stars in a disk by Massive Compact Objects (Machos) in the same
disk. For the more restricted case where the disk is self-gravitating and the
stars and Machos have the same distribution function, I find $\tau =
2\VEV{v^2}/c^2\sec^2 i$ where $\VEV{v^2}$ is the mass-weighted vertical
velocity dispersion, and $i$ is the angle of inclination. This result does not
depend on any assumptions about the velocity distribution. As an example, if
stars within the bar of the Large Magellanic Cloud (LMC) account for the
observed optical depth $\tau\sim 8\times 10^{-8}$ as has recently been
suggested, then $v\gsim 60\,\kms$. This is substantially larger than the
measured dispersions of known LMC populations.
