  We study the odd-frequency Cooper pairs formed near the surface of superfluid
3He. The odd-frequency pair amplitude is closely related to the local density
of states in the low energy limit. We derive a formula relating explicitly the
two quantities. This formula holds for arbitrary boundary condition at the
surface. We also present some numerical results on the surface odd-frequency
pair amplitude in superfluid 3He-B. Those analytical and numerical results
allow one to interpret the midgap surface density of states, observed recently
by transverse acoustic impedance measurements on superfluid 3He-B, as the
manifestation of the surface odd-frequency state.
