We discuss the properties of D-brane configurations in the matrix mode
l of the type IIB superstring recently proposed by Ishibashi, Kawai, K
itazawa and Tsuchiya. We calculate the central charges in the supersym
metry algebra at infinite N and associate them with one- and five-bran
es present in IIB superstring theory. We consider classical solutions
associated with static three- and five-branes and calculate their inte
ractions at one loop in the matrix model. We discuss some aspects of t
he matrix-model formulation of the IIB superstring. (C) 1997 Published
by Elsevier Science B.V.