We consider the general properties of central charges of 0-branes and assoc
iated duality invariants, in view of their double role, on the bulk and on
the world volume (quantum mechanical) theory. A detailed study of the BPS c
ondition for the mass spectrum arising from toroidal compactifications is g
iven for 1/2, 1/4, and 1/8 BPS states in any dimension. As a by-product, we
retrieve the U-duality invariant conditions on the charge (zero mode) spec
trum and the orbit classification of BPS states preserving different fracti
ons of supersymmetry. The BPS condition for 0-branes in theories with 16 su
persymmetries in any dimension is also discussed. [S0556-2821(99)01716-6].