Hyperprolactinemia is often observed in lymphocytic hypophysitis (LYH). To clarify the possible autoimmune pituitary involvement in patients with apparently idiopathic hyperprolactinemia we investigated the presence of antipituitary antibodies (APA) in hyperprolactinemic patients with idiopathic hyperprolactinemia and in those with prolactinoma. Sixty-six hyperprolactinemic patients (52 F, 14 M age range 28-42 years, group 1) were studied. Of them, 34 out of 66 showed clinical features of hyperprolactinemia and subsequently underwent cabergoline therapy; the 32 out of 66 patients without symptoms of hyperprolactinemia did not receive cabergoline therapy. Moreover, 32 patients (24 F/8M, age range 23-44 years) with hyperprolactinemia due to microprolactinoma (group 2) were also studied. APA, by immunofluorescence method, and anterior pituitary function were evaluated in both groups of patients. APA were present in 17 out of 66 (25.7%) patients in group 1 with titers ranging from 1/16 to 1/64. All patients of group 2 were considered APA negative because these antibodies were found at low titer (<or=1:4) only in five of them. With regard to the function of other pituitary hormones, all APA-negative patients in group 1 and in group 2 showed a normal pituitary function; instead, a partial anterior pituitary impairment was observed in 6 out of 17 (35.3%) APA-positive patients. In asymptomatic patients with apparently idiopathic hyperprolactinemia, APA detection could be useful to disclose forms of potential/subclinical stage of LYH. A future longitudinal study of these patients submitted to cabergoline therapy or free of therapy may be helpful to clarify this assumption.