Twelve women with galactorrhea-amenorrhea and prolactin levels greater than 100 ng/ml were evaluated with dynamic pituitary challenge testing. Forty-two per cent of the patients had positive findings on polytomography and subsequent surgical confirmation of a pituitary tumor. Patients with tumors had a delayed elevation of growth hormone (GH) and cortisol following induction of insulin hypoglycemia. Patients had increased thyroid-stimulating hormone levels after injection of thyrotropin-releasing factor, but showed blunting of prolactin secretion. Patients with tumors had decreased basal levels of GH and showed a blunted response to luteinizing hormone-releasing hormone (LRF) stimulation. These patients had normal elevations of follicle-stimulating hormone after LRF challenge. Patients with tumors showed a delay in elevation of GH levels following l-dopa treatment. They also failed to show prolactin suppression following this treatment. There are consistently predictive changes that occur in pituitary functions in the presence of a pituitary tumor. However, absolute prolactin levels and sellar polytomography are more reliable in diagnosing the presence of a pituitary tumor in the patient with galactorrhea-amenorrhea.