  We study D-branes in the bosonic closed string theory whose automorphism
group is the Bimonster group (the wreath product of the Monster simple group
with Z_2). We give a complete classification of D-branes preserving the chiral
subalgebra of Monster invariants and show that they transform in a
representation of the Bimonster. Our results apply more generally to self-dual
conformal field theories which admit the action of a compact Lie group on both
the left- and right-moving sectors.
