In Britain one person in every hundred is a diabetic and knows it. A further one in a hundred is a diabetic and doesn'know it - yet. Diabetes appears to run in families yet two thirds of all diabetics report no previous family history. Although it's one of the oldest diseases known to man its cause remains a mystery. Until 1921 diabetes was a painful killer - often within a few weeks in children, usually within two years in adults. Then, nearly 50 years ago, two young Canadian scientists, Frederick Banting and Charles Best , made one of the most dramatic discoveries in the whole history of medicine. They isolated a substance called Insulin which today keeps some ten million diabetics alive. In the programme Dr Charles Best , now aged 70, describes that dramatic discovery. Among the diabetics taking part: TREVOR HUDDLESTON Bishop of Stepney TONY MERCER of Black and White Minstrel fame SUE LLOYD, the actress, and ANDY PENMAN , the Scottish International footballer Interviewer DR STEPHEN BLACK Produced by PHILIP DALY