This work is supported by USPHS Grant CA 48129 and a grant from the U. S. Army Medical Research and Materiel Command DAMD 17-96-6254. The content of this publication does not necessarily reflect the position of the government and no official endorsement of any equipment and product of any companies mentioned in the publication should be inferred. The authors are grateful to Charles E. Metz, Ph. D. for the LABROC programs.