From a previously reported 5-year screening programme of 6,956 47-49-year-old Malmö males, a series of 41 subjects with early-stage Type 2 (non-insulin-dependent) diabetes mellitus and 181 subjects with impaired glucose tolerance were selected for prospective study and to test the feasibility aspect of long-term intervention with an emphasis on life-style changes. A 5-year protocol, including an initial 6-months (randomised) pilot study, consisting of dietary treatment and/or increase of physical activity or training with annual check-ups, was completed by 90% of subjects. Body weight was reduced by 2.3-3.7% among participants, whereas values increased by 0.5-1.7% in non-intervened subjects with impaired glucose tolerance and in normal control subjects (p less than 0.0001); maximal oxygen uptake (ml.min-1.kg-1) was increased by 10-14% vs decreased by 5-9%, respectively (p less than 0.0001). Glucose tolerance was normalized in greater than 50% of subjects with impaired glucose tolerance, the accumulated incidence of diabetes was 10.6%, and more than 50% of the diabetic patients were in remission after a mean follow-up of 6 years. Blood pressure, lipids, and hyperinsulinaemia were reduced and early insulin responsiveness to glucose loading preserved. Improvement in glucose tolerance was correlated to weight reduction (r = 0.19, p less than 0.02) and increased fitness (r = 0.22, p less than 0.02). Treatment was safe, and mortality was low (in fact 33% lower than in the remainder of the cohort).(ABSTRACT TRUNCATED AT 250 WORDS)