OBJECTIVE To assess the frequency of hyperprolactinemia and its possible clinical significance in patients with systemic lupus erythematosus (SLE). METHODS Concentrations of prolactin (PRL) were determined in 63 consecutive patients with SLE by an immunoradiometric assay. Antinuclear antibodies, anti-DNA, ribonucleoprotein, Sm, Ro, La, and anticardiolipin antibodies were determined by standard techniques. PRL concentrations were correlated with SLE clinical and serological activity. RESULTS Elevated serum concentration of PRL (> 20 ng/ml) were found in 10 of 63 (15.9%) patients [21 to 57 ng/ml, mean (SD) 35.6 (13.4)]. No direct correlation between PRL levels and clinical disease activity of SLE was found (Pearson correlation r = -0.186, NS). In addition, hyperprolactinemia was not associated with serological activity. CONCLUSIONS Mild hyperprolactinemia is present in a subset of patients with SLE but its clinical significance is still uncertain.