It describes the toxicologist's role as expert witness during pretrial discovery and preparation, direct examination, and cross examination. Experts must realize that their demeanor on the witness stand may mean the difference between the jury's accepting or rejecting their testimony. Experts should maintain direct eye contact with jurors and speak in normal conversational tones. Scientific terms should be made understandable to the lay person. Experts should not try to guess at an answer during cross-examination but should respond that they do not know the answer. Mistakes should be admitted and impartiality during testimony maintained. About 30 references are cited.