  We prove a duality formula for certain sums of values of poly-Bernoulli
polynomials which generalizes dualities for poly-Bernoulli numbers. We first
compute two types of generating functions for these sums, from which the
duality formula is apparent. Secondly we give an analytic proof of the duality
from the viewpoint of our previous study of zeta-functions of Arakawa-Kaneko
type. As an application, we give a formula that relates poly-Bernoulli numbers
to the Genocchi numbers.
