A new first-order action for type IIB Dirichlet 3-brane is proposed. I
ts form is inspired by the superfield equations of motion obtained rec
ently from the generalized action principle. The action involves auxil
iary symmetric spin tensor fields. It seems promising for a reformulat
ion of the generalized action in a structure most adequate for investi
gating the extrinsic geometry of the super-3-brane, but also for furth
er studies of string dualities. (C) 1997 Published by Elsevier Science
B.V.