The importance of a detailed quantitative assessment of the existing dietary and nutritional status of a community before the planning of an intervention programme, as well as the subsequent evaluation of the short and long-term effectiveness of the programme, are emphasized. Practical problems surrounding the measurement of dietary intake of individuals and communities are considered and details of improved methodologies provided. Ways of assessing nutritional health status by clinical examination, anthropometry, morphology and biochemistry are also dealt with and their individual shortcomings discussed. Another feature which is emphasized is the close relation between nutrient intake and the pattern of infection in determining nutritional status. Specific quantitative examples are provided from prospective longitudinal studies which have been carried out in Uganda and The Gambia. The integration of different types of health data into the formulation of an integrated preventive nutritional programme is also reviewed.