Brazil, has for four years carried out a well-designed large- scale nutrition programme which combines primary health care with food supplementation. However, the nutritional aspects of this programme have not been evaluated. Failure to evaluate nutrition intervention is common in most countries, partly because of the lack of interest of governments, and mainly because of the lack of a methodology for assessing their effectiveness. The Brazilian programme has provided a stinrulus and an opportunity to evaluate the results of such inter- ventions. The objective of the present study is to contribute to the methodology for evaluating nutrition interventions. This study reports a follow-up of 4041 children aged 6 to 36 m:mths at admission to the programme, from slum areas in the city of Salvador, North East Brazil. \\eight and height were measured peri- odically for four years; the exact ages of the children were available from birth certificates. The effectiveness of the programme is evaluated in terms of changes in the nutritional status before and after supplementation. Cohorts were established for the analyses, according to the nutri- tional status, age of admission and period of supplementation. Commonly used anthropometric methods are tested and modifi- cations presented. The U.S.A. National Center for Health and Statistics (NCHS) growth curves are adopted as standards