The role of diet in human insulin-dependent diabetes mellitus (IDDM) has not been properly examined, mainly due to a lack of reliable markers to identify prospective diabetics and the difficulties in obtaining accurate and representative dietary information. Nonetheless, there is some circumstantial evidence suggesting a role for diet in human IDDM. The validity of this relationship in humans must await a sufficiently large, well designed prospective study or the discovery of better markers for diabetes predisposition. The recent availability of the spontaneously diabetic BB rat has permitted prospective studies under controlled conditions which indicate diet, particularly dietary proteins, such as wheat gluten or cow's milk proteins may be prerequisites for maximum expression of the insulin-dependent syndrome in these animals. The early suckling and/or post-weaning period appears to be important and may be the crucial time when these proteins or portions of them pass the gastrointestinal barrier and initiate a process, possibly immunological, which results in destruction of the beta cells of the pancreas.