1. G. Simmons, P. R. Clapham, L. Picard, Virology Group, Chester Beatty Laboratories, Institute of Cancer Research, 237 Fulham Road, London SW3 6JB, UK.
2. R. E. Offord, Départment de Biochimie Médicale, Centre Médical Universitaire, 9 Avenue de Champel, 1211 Geneva 4, Switzerland, and Gryphon Sciences, 250 East Grand Avenue, Suite 90, South San Francisco, CA 94080, USA.
3. M. M. Rosenkilde and T. W. Schwartz, Laboratory for Molecular Pharmacology, Rigshospitalet 6321, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
4. R. Buser, T. N. C. Wells, A. E. I. Proudfoot, Geneva Biomedical Research Institute, GlaxoWellcome Research and Development SA, 14 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland.