 Keen assisted Pickering over several years on a large project studying hypertension in patients with diabetes and their first-degree relatives.In 1953, he began collaborating with Robert Daniel Lawrence, who headed the diabetes clinic at King's College Hospital, and spent seven years there studying diabetes and its long-term complications.He travelled to Bethesda, Maryland, in 1960 for a year-long research fellowship at the National Institutes of Health, where he experimented with insulin assays and early attempts to isolate pancreatic islets.