A population-based longitudinal study of abnormal glucose tolerance in the adult Maltese, carried out within the WHO-assisted National Diabetes Programme, has recently been completed. During the 6-year interval abnormal as compared to normal glucose tolerance was found to be related to a significantly higher mortality: the age-adjusted relative risks of death were 3.3 times in diabetic females and greater than 2 times in IGT and diabetic males. In the repeat epidemiological survey 1422 subjects (66.8% of the initial sample) were reinvestigated with the oral GTT being interpreted according to WHO's 1985 recommendations. The age-standardised prevalence rates, in the 35-69-year-old males and females, were respectively 12.89% and 13.24% for IGT and 9.07% and 10.77% for diabetes. These gradually increased after age 40, IGT peaking in the 60+ year groups and diabetes 10 years later. Heredity (especially diabetes in close relatives) seemed a major influence, whilst excess body weight appeared the more important associated environmental factor. The incidence levels (% per annum) of diabetes during the interval were 0.71 for normoglycaemics and 5.1 for IGTs; this seven times higher risk in the latter was slightly lower in females than males, but significantly higher in the less than 60-year-olds compared to older subjects. Of the initial IGTs 36% remained IGT and 33% reverted to normal glucose tolerance, whilst 11% of the initial normoglycaemics deteriorated to IGT. The determinants more strongly influencing worsening of glucose tolerance were age (greater than 50 years), baseline glycaemia (fasting greater than 5.5 mmol/l and a 2-h post-load glycaemia greater than 9.5 mmol/l) and initial body mass index (greater than 27 kg/m2). In conclusion the data permit a better insight into the natural history of, and risk factors for, disturbed glucose tolerance in this community.