Introduction The normal diet and growth patterns of most animals are so far removed from man as to make extrapolation of data across species boundaries a difficult, if not impossible, exercise. The phylogenetic argument that sub-human primates are evolutionarily nearer man does not necessarily mean that they are the most useful as animal models. The nutritional requirements of laboratory monkeys have recently been reviewed by Harris (1970) and Kerr (1972). Monkeys might be of value in studying disorders of human nutrition and development, but their usefulness depends on establishing normal figures. This paper presents some data on the growth and development of infant rhesus monkeys (Macaca mulatta).