  In the first part of this letter, we analyse the supergravity dual
descriptions of six-dimensional field theories realized on the worldvolume of
(p,q) five-branes (OD5 theory). We show that in order for the low-energy gauge
theory description to be valid the theta parameter must be rational. Irrational
values of theta require a strongly coupled string description of the system at
low-energy. We discuss the phase structure and deduce some properties of these
theories. In the second part we construct and study the supergravity
description of NS5-branes with two electric RR field, which provides a dual
description of six-dimensional theories with several light open D-brane
excitations.
