On a generalized complex manifold, there is an associated definition of a generalized holomorphic bundle, introduced by Gualtieri. In the case of an ordinary complex structure, this notion yields an object which we call a co-Higgs bundle, and we consider the B-field action of a closed form of type (1, 1), both local and global. The effect makes contact with both Nahm's equations and holomorphic gerbes. (C) 2010 Elsevier B.V. All rights reserved.