Despite a marked increase in the prescription of oral nutritional supplements (ONS) in the community (Department of Health, 1991-7), there is still uncertainty about the value of their use in patients with different diseases. To answer questions about the effects on ONS on body weight and structure, spontaneous food intake and body function, a critical systematic review was undertaken (Stratton & Elia, 1999a). Eighty-four trials were reviewed (forty-five randomized, thirty-nine non-randomized: 2,570 patients; diagnoses including chronic obstructive pulmonary disease, Crohn's disease, cystic fibrosis, human immunodeficiency virus and acquired immune deficiency syndrome and cancer). Most studies (83 %) were conducted in patients living at home. The supplements were typically mixed macronutrients in liquid form, providing < 0.42-10.5 MJ/d for 1 week-2 years. The studies reviewed in patients with predominantly chronic conditions living in the community suggested that: (1) ONS produce demonstrable clinical (including functional) benefits, but the nature and extent of these benefits varies with the underlying chronic condition; (2) ONS increase total energy intake with > 50 % of the energy from ONS typically additional to that from habitual food intake; (3) improvements in body weight, total energy intake and body function following ONS appear to occur more frequently in individuals with a BMI < 20 kg/m2 than in those with a BMI > 20 kg/m2.