In a general practice-based screening survey, 1040 (63.3%) of a randomly selected sample of 1644 people over the age of 40 years were examined for diabetes mellitus (DM) and hypertension (HT). Glucose intolerance was assessed by a single 2 h post-load blood glucose estimation and HT (diastolic blood pressure greater than or equal to 95mmHg by a single blood pressure reading) or being on anti-hypertensive treatment. The sample included 41 patients (2.1%) with known DM and 135 (12.5%) with known HT. Screening identified 27 (2.6%) new diabetics (16 women) and 43 subjects (4.1%) with impaired glucose tolerance (30 women). A further 30 known diabetics over the age of 40 and 12 diabetics under 40 were registered at the practice. The estimated prevalence of diabetes in the over 40s was 4.6% and in all ages was 1.6%. DM appeared to affect Afro-Caribbeans more commonly than Caucasians among those examined (5.9% versus 2.6%) though this difference did not reach statistical significance (z = 1.1106, p = 0.134). A total of 190 subjects (17.5%) were found to have HT, of whom 55 (5.1%) were newly diagnosed; 10.2% of the sample were on anti-hypertensive treatment, and in 79.3% of these the blood pressure was well controlled (diastolic less than 100 mmHg). HT was more common among known diabetics with a prevalence of 35.4%, of whom one-third were previously undiagnosed. HT affected Afro-Caribbeans significantly more commonly than Caucasians (z = 4.206, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)