D-branes on K3-fibrations

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