D-branes on K3-fibrations

B-type D-branes are constructed on two different K3-fibrations over P-1 using boundary conformal field theory at the rational Gepner points of these models. The microscopic CFT charges are compared with the Ramond charges of D-branes wrapped on holomorphic cycles of the corresponding Calabi-Yau manifold. We study in particular D4-branes and bundles localized on the K3 fibers, and find fr om CFT that each irreducible component of a bundle on K3 gains one modulus upon fibration over P-1. This is in agreement with expectations and so provides a further test of the boundary CFT approach to D-brane physics. (C) 2000 Elsevier Science B.V. All rights reserved.