A new very low energy formula diet containing 1560 kJ (373 kcal) per day was employed in the treatment of 49 obese patients. The treatment, of 4 weeks duration, included aerobic physical exercise and behavioural intervention. This kind of therapy resulted in a significant decrease (P less than 0.001) of both weight (-10.60 +/- 0.46 kg) and body mass index (-3.36 +/- 0.16). The fat stores represented 90.5 per cent of weight loss in women and 60.0 per cent of weight loss in men. The first very low energy formula diet produced in Czechoslovakia proved to be an efficient and safe tool for the treatment of obesity, positively affecting high blood pressure, lipid and carbohydrate metabolism in the absence of serious side-effects.