Data are presented from a recent longitudinal study of dietary habits of English children aged 11-13 y, in relation to various factors which may have influenced the estimations of intake. A knowledge of such relationships may aid the design and interpretation of this and other dietary surveys. The factors studied included survey fatigue, learning effect, season of the year, day of the week and the subjects' knowledge of the study's purpose. Generally the relationships found were of minor importance, but the variable influence of some of these factors is apparent from a study of the relevant literature. This is one reason why dietary survey methodology is resistant to simplification. It is concluded that the dietary survey method used was adequate for the purpose of the study.