The pattern of prescribing in a diabetic clinic population extending over a 25 year period is examined. The number of patients studied, 4355, was divided into three categories according to age at onset of diabetes, those diagnosed before 15 years of age, those diagnosed between 15 and 45 years and those diagnosed after the age of 45 years. A reduction in the proportion of maturity-onset diabetics, in whom oral hypoglycaemic agents were used, is noted, when treatment prior to 1970 is compared with that post-1970. This reduction, from 36% of the total population prior to 1970 to 29% after 1970 was accompanied by an increase in the proportion treated by diet alone for the same period of from 17% to 30%. For the past three years metformin has replaced phenformin as the biguanide of choice in the clinic.