Ethical implications of physician involvement in lawsuits on behalf of the tobacco industry.

The statements of physicians who serve as expert witnesses for the tobacco industry reveal subtle but significant problems. Some expert testimony obfuscates the important issues, and some initially reasonable statements later evolve into extreme positions during cross-examination. Such statements fall into a "gray area" of professional ethics, potentially misleading juries and adversely affecting professional integrity. Medical associations can and should strongly enforce professional standards that do not tolerate tobacco industry influence on physician expert witnesses.