We experienced a 22-year-old diabetic patient with prolactinoma. After hypophysectomy, he developed easy fatigability, polydipsia and polyuria in July of 1992. He visited us and was diagnosed as having diabetes mellitus. He was admitted to our hospital in December of 1992. Initially, he was treated with diet and oral hypoglycemic agents. His plasma glucose was well controlled by diet and exercise therapy. Because of the residual pituitary adenoma with increased plasma prolactin levels, he was

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... eated with bromocriptine. Soon thereafter, his plasma prolactin level decreased to within normal range. We examined glucose tolerance before and during the bromocriptine treatment. During this treatment, glucose intolerance and the plasma insulin response to 75g OGTT improved. These data suggest that hyperprolactinemia may affect insulin secretion.