  We compute an SL(6,Z) invariant partition function for the chiral two-form of
the M theory fivebrane compactified on the six-torus. From a manifestly SL(5,Z)
invariant formalism, we prove that the partition function has an additional
SL(2,Z) symmetry. The combination of these two symmetries ensures SL(6,Z)
invariance. Thus, whether or not a fully covariant Lagrangian is available, the
fivebrane on the six-torus has a consistent quantum theory.
