Argyrophil nucleolar organizer regions (AgNORs) were morphometrically evaluated in rat anterior pituitaries of control and oestrogenized rats using an automatized (LCJCIA M — Laboratory Universal Computer Image Analysis Micro) and a non-automatized approaches to investigate not only the sensitivity and effectiveness of the automatized procedure but also the morphology of AgNORs in oestrogen-induced rat anterior pituitary hyperplasia. In the experimental oestrogen-induced rat anterior pituitary hyperplasia, the image analysis system LUCIA M was compared to a non-automatized morphometric procedure and proved to be very efficient and yielded analogical results. The AgNOR morphology in the oestrogenized pituitaries was characterized by an increase of the total AgNOR area and clustering of AgNORs in the large nucleoli.