&NA;A 39‐year‐old woman with secondary amenorrhea and visual field defects underwent craniotomy for a large pituitary tumor that was hormonally silent according to measurement of plasma hormone levels and immunohistochemical analysis. During the preoperative investigation, bromocriptine was administered for 1 month, but there was no change in the tumor size as seen on computed tomographic scans. One month after surgery, visual field defects recurred, and a tumor mass comparable to the preoperative state was found on computed tomographic scan. The tumor size gradually diminished during treatment with CV 205‐502, a tricyclic benzoquinoline which stimulates mainly D2receptors and is better tolerated than bromocriptine. The visual fields were completely normalized after 3 months of treatment with the drug, and surgical management of the tumor mass was no longer considered to be necessary. Thus, as in many similar cases, the hormonally silent pituitary tumor in this patient proved unresponsive to bromocriptine treatment. In contrast. the tumor was reduced by therapy with CV 205‐502, a drug that is better tolerated and might permit a more intense stimulation of D2receptors. (Neurosurgery25:948‐950, 1989)