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Prolactin hypersecretion from a pituitary adenoma usually results in a serum prolactin level less than 1,000 ng/ml. During therapy with a dopamine agonist, prolactin levels usually normalize and the tumors shrink substantially. In the past few years, we have seen three men who presented with serum prolactin levels greater than 10,000 ng/ml. All presented with large tumors, visual field deficits, and hypogonadotropic hypogonadism. All other pituitary hormones were normal. In all three patients, significant tumor shrinkage was achieved with improvement or resolution of headaches and visual field deficits. None of our patients has been able to achieve a normal prolactin or testosterone. A literature review identified 32 patients with prolactin levels of more than 10,000 ng/ml. Twenty-six (81%) were males. Most had large tumors, headaches and visual field defects. Even with the addition of surgery and/or radiation therapy to medical therapy, normalization of serum prolactin occurred in only six patients (19%) and only one man achieved a normal testosterone. We conclude that in patients with massive prolactin hypersecretion, therapy with a dopamine agonist will lead to tumor shrinkage and improvement of mass effects, but usually does not normalize prolactin or testosterone. Rather than waiting for maximal prolactin reduction, we would recommend early institution of testosterone replacement therapy.