Among the environmental factors leading to type 1 diabetes in childhood, the most important are certain viral infections and possibly some dietary factors. Among the latter cow's milk proteins are of special interest. They have been shown to be involved in the pancreatic beta-cell lesion in animal experiments. In humans there are some indications of a role of early exposure to cow's milk proteins as a risk factor for later type 1 diabetes. The hypothesis has not been confirmed, but a randomized, controlled double-blinded intervention trial should provide a definite answer.