Antigen expression in type 1 (insulin-dependent) diabetes may depend on the functional state of beta cells. At birth, beta cells are immature, produce only a basal amount of insulin, and are unresponsive to glucose--but are sensitive to glucagon and arginine. beta cells of spontaneously diabetic BB rats were stimulated for the first 6 days after birth by glucose with glucagon or arginine to accelerate beta cell maturation, and possibly to induce antigen expression and tolerance. Over the first 200 days of life, only 23% of glucose and glucagon-treated BB rats, and 20% of glucose and arginine-treated BB rats developed diabetes, compared with 65% of untreated controls. This finding may explain the observation that children of mothers who have type 1 diabetes are three times less likely to develop the disease than children of fathers with type 1 diabetes. Earlier maturation of beta cells during the diabetic pregnancy may protect against diabetes in later life.