  Making use of a Howe duality involving the infinite-dimensional Lie
superalgebra $\hgltwo$ and the finite-dimensional group $GL_l$ we derive a
character formula for a certain class of irreducible quasi-finite
representations of $\hgltwo$ in terms of hook Schur functions. We use the
reduction procedure of $\hgltwo$ to $\hat{gl}_{n|n}$ to derive a character
formula for a certain class of level 1 highest weight irreducible
representations of $\hat{gl}_{n|n}$, the affine Lie superalgebra associated to
the finite-dimensional Lie superalgebra $gl_{n|n}$. These modules turn out to
form the complete set of integrable $\hat{gl}_{n|n}$-modules of level 1. We
also show that the characters of all integrable level 1 highest weight
irreducible $\hat{gl}_{m|n}$-modules may be written as a sum of products of
hook Schur functions.
