1. W. K. Hong is in the Department of Thoracic/Head and Neck Medical Oncology, University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Box 80, Houston, TX 77030, USA. M. B. Sporn is in the Department of Pharmacology and Norris Cotton Cancer Center, Dartmouth Medical School, 7650 Remsen, Hanover, NH 03755, USA.