Two different generalization of Perron-Frobenius theory to the matrix
pencil $Ax=\lambda Bx$ are discussed, and their relationships
are studied. In one generalization, which was motivated
by economics, the main assumption is that
$(B - A)^(-1)A$ is nonnegative. In the second generalization, the
main assumption is that there exists a matrix $X\le 0$
such that $A=BX$. The equivalence of these two
assumptions when B is nonsigular is considered.
For $\rho(|B^(-1)A|)<1$, a complete characterization,
involving a condition on the digraph of $B^(-1)A$, is
proved. It is conjectured that the characterization holds for $\rho(B^(-1)A)<1$,
and partial results are given for this case.