Sixty-two moderately obese (body mass index = 34.8), but normotensive females were treated with a balanced hypocaloric diet providing 1,600 kcal/day and either a 6.5 g dietary fibre supplement or placebo in a randomized, double-blind, parallel group design. During a 12-week treatment programme, weight loss was similar in both groups (4.1 and 4.4 kg, respectively). Initially the blood pressure was 123/76 mmHg in the fibre group compared with 124/74 mmHg in the placebo group (p less than 0.05). In the fibre-treated group a significant fall in diastolic blood pressure by 4 mmHg was found (p less than 0.05). No significant change was seen in the placebo group. It is suggested that dietary fibre may affect blood pressure independently of weight change.