A total of 41 patients with hypertension were identified in a survey of 732 healthy factory workers. Twenty-three of these individuals were receiving antihypertensive medication, whereas 18 cases were newly discovered. Plasma glucose and insulin responses to oral glucose and fasting plasma triglyceride (TG), cholesterol, and high-density-lipoprotein (HDL) cholesterol concentrations of these 41 individuals were compared with those of 41 other factor workers, with normal blood pressure, matched with the hypertensive group in terms of gender, age, degree of obesity, job in the factory, and leisure-time activity. Patients with hypertension had significantly higher plasma glucose (P less than 0.05) and insulin (P less than 0.05) concentrations in response to oral glucose, as well as a higher plasma TG concentration (P less than 0.05). Similar findings were obtained when the treated and untreated hypertensive groups were analysed separately and compared with their respective control groups. However, there were no differences between the treated and untreated hypertensive groups. Ninety per cent of the normotensive group had a plasma insulin concentration of less than 500 pmol l-1 2 h after the glucose load. Using this value as the criterion for definition of hyperinsulinaemia, 41% of the patients with high blood pressure were hyperinsulinaemic. In addition to meeting this cut-off point, the patients with hypertension and hyperinsulinaemia were also glucose intolerant and dyslipidaemic. In conclusion, approximately 50% of an unselected group of patients with hypertension were hyperinsulinaemic. Insulin levels were comparable in treated and untreated patients with high blood pressure, and hyperinsulinaemic patients also tended to be glucose intolerant and dyslipidaemic.