  We study gauge theories on noncommutative tori. It was proved in [5] that
Morita equivalence of noncommutative tori leads to a physical equivalence
(SO(d,d| Z)-duality) of the corresponding gauge theories. We calculate the
energy spectrum of maximally supersymmetric BPS states in these theories and
show that this spectrum agrees with the SO(d,d| Z)-duality. The relation of our
results with those of recent calculations is discussed.
