Between 1760 and 1845, approximately 350 criminal defendants alleged some form of mental impairment as an excuse for their actions. However, only 75 used medical witnesses. Before 1825, almost half the medical witnesses were testifying about friends or former patients. In the second quarter of the 19th century, a change in professional stance occurred, and the medical professional and the accused person began their association when the accused person was in detention awaiting trial or in confinement to a madhouse. Gilbert McMurdo, Surgeon of Newgate Jail, appeared in 19 trials, including that of Daniel McNaughtan. However, his forensic experience does not seem to have been a major part of his professional life. The medical specialists appearing as witnesses represented all of the major specialties. Offenses were mainly property offenses, although medical witnesses were increasingly used in cases involving personal offenses during the latter part of the study period. The testimony of the medical specialists rarely departed in any obvious way from that of law witnesses until the trial of Edward Oxford in 1840. Nevertheless, medical specialists were increasingly being recognized as an important force in insanity trials. Tables, footnotes, and excerpts of testimony.