Certain limits of the duality between M-theory on T-5/Z(2) and IIB on
K3 are analyzed in Matrix theory. The correspondence between M-theory
five-branes and ALE backgrounds is realized as three-dimensional mirro
r symmetry. Non-critical strings dual to open membranes are explicitly
described as gauge theory excitations. We also comment on Type IIA on
K3 and the appearance of gauge symmetry enhancement at special points
in the moduli space. (C) 1998 Published by Elsevier Science B.V.