Forty‐one women with oligo‐menorrhoea and/or galactorrhoea were subjected to hypothalamic pituitary‐thyroid testing in an attempt to establish the presence or absence of an underlying pituitary microadenoma. They were divided into two groups in accordance with the serum level of prolactin (PRL): Group I (N = 25, mean ± SE 17.6 ± 1.5 ng/ml) and Group II (N = 16, 102.8 ± 29.7 ng/ml). The dynamic tests performed were a TRH test, a stimulation test with metoclopramide (MCP) and a suppression test with bromocriptine. The results of these tests were compared with those obtained in nine normal women and eleven patients with surgically proved pituitary microadenoma. Radiologically abnormal pituitary fossas were found in ten subjects from Group I and in fourteen from Group II. All patients were euthyroid. A persistently elevated serum TSH in response to TRH was observed in patients of Group II suggesting an hypothalamic abnormality and a progressive decrease in the 120‐min use of serum T3 was n