Various cow-milk preparations have, with some variation, been reported to be diabetogenic in two animal models of insulin-dependent diabetes mellitus (IDDM), the BioBreeding (BB) rat and the nonobese diabetic (NOD) mouse. However, the suggestion of an inverse relationship between breast-feeding and IDDM based on epidemiological studies, remains controversial. There is a significant positive correlation between consumption of unfermented milk protein and incidence of IDDM in data from various countries. Conversely, a possible negative relationship is observed between breast-feeding at age 3 mo and IDDM risk. Diet may be an important permissive factor in the development of IDDM.