John Fletcher Ackroyd, a physician at St Mary's Hospital, Paddington, carried out research into drug hypersensitivity and allergy. He was born in London, the son of George William Ackroyd, a minister of religion, and Margaret Bull, the daughter of an antique dealer. He was educated at Bristol Grammar School, and then went on to Bristol University. He completed his clinical studies at Bristol Royal Infirmary. He held house posts at the Royal Infirmary and General Hospital in Bristol, and was then appointed as a junior lecturer in pathology at the University of Bristol.
In May 1942 he was appointed as an assistant pathologist at St Mary's Hospital, London, and subsequently as a clinical assistant. In October 1945 he was appointed as an assistant to the medical unit, St Mary's Hospital Medical School. From 1948 he was a senior lecturer in medicine at St Mary's.
His research work began with his study of drug-induced thrombocytopenia. With his precise and consistent approach, he ensured that all contaminants and excipients were systematically tested, as well as the named agents. Apart from his research work, he was also an occasional clinician, both in and out patients and occasionally in charge of medical unit beds under Sir George Pickering [Munk's Roll, Vol.VII, p.464]. As the years went by John stopped direct patient care except that, after retiring from his post in the medical unit, he worked in the allergy clinic with special interests in drug associated disease.
He was the first to establish that the rashes seen after administration of ampicillin were nearly always in patients with infectious mononucleosis. He collected a number of patients and rechallenged these with ampicillin after recovery. All repeat tests were negative, so did not show a true 'ampicillin sensitivity', except in the patients with active viral infection. Subsequently it became recognised that it was almost diagnostic of the disease to produce a rash with ampicillin.
He took considerable interest in the students to whom he taught immunology. If they had emotional problems he acted as father figure and confidante. While he was able to walk to the library, he continued to seen about the Praed Street complex for so long that some of those who had known him over many years were unsure whether it really was John Ackroyd or just a ghostly reminder of a most interesting man.