Certain developments in the agricultural and food sciences have far-reaching implications for society and the environment, which suggest the need to examine their ethical acceptability as a standard component of technology assessment. Such considerations have led to the emergence of a new academic discipline, food ethics. The present paper describes how ethical theory may be applied to the analysis of the impacts of prospective food biotechnologies to assess potential effects on four 'interest groups', i.e. consumers, producers, treated organisms and the biota (fauna and flora). The principles which structure the framework used, i.e. the ethical matrix, are adapted to the field of agriculture and food from those applied in medical ethics. Use of the ethical matrix is illustrated by applying it to the specific case of bovine somatotrophin, the genetically-engineered protein hormone which is injected into lactating cattle to increase their milk yields. Ethical analysis is seen to depend on a number of critical requirements, i.e. scientific data, non-scientific evidence and predictions, suitably-qualified assessors ('competent moral judges'), the 'world-views' of the assessors and application of the precautionary principle to cope with 'uncertainty'.