The aim of this study was to assess the effect of Silitidil, a standardized extract of milk thistle, on the serum levels of prolactin in female rats. A 14-day treatment with Silitidil (25-200 mg/kg, per os), a standardized extract of Silybum marianum fruits (milk thistle), increased, in a dose dependent manner, the serum prolactin levels in female rats. Galega (200 mg/kg, per os) given alone neither modified the basal levels of prolactin nor increased further serum prolactin levels when associated with Silitidil. Bromocriptine (1 mg/kg, per os) significantly reduced the high serum prolactin levels induced by Silitidil (200 mg/kg, per os). The results show that the extract of S. marianum fruits significantly increases prolactin levels in female rats; this effect is not potentiated by galega and seems to involve, at least in part, dopamine D2 receptors.