  The double-layer potential plays an important r$\hat{\rm o}$le in solving
boundary value problems of elliptic equations. Here, in this paper, we aim at
introducing and investigating double layer potentials for a generalized
bi-axially symmetric Helmholtz equation. By using some properties of one of
Appell's hypergeometric functions in two variables, we prove limiting theorems
and derive integral equations concerning a denseness of double-layer
potentials.
