  We consider the asymptotic behavior of the incomplete gamma functions
gamma(-a,-z) and Gamma(-a,-z) as a goes to infinity. Uniform expansions are
needed to describe the transition area z~a in which case error functions are
used as main approximants. We use integral representations of the incomplete
gamma functions and derive a uniform equation by applying techniques used for
the existing uniform expansions for gamma(a,z) and Gamma(a,z). The result is
compared with Olver's uniform expansion for the generalized exponential
integral. A numerical verification of the expansion is given in a final
section.
