In 3 groups of women (1. with pathological hyperprolactinemia, but low estradiol level--19 patients; 2. with pathological hyperprolactinemia, but high estradiol level--17 patients; 3. 16 healthy control women) the level of prolactin, estradiol, cortisol, total cholesterol, triglycerides and apolipoproteins A-I, A-II and B in serum was estimated together with routine clinical examination. In both hyperprolactinemic groups a significant decrease of apolipoprotein A-I and A-II was found, while in the group with high estradiol also a significant decrease of apolipoprotein B was observed. It is suggested that the increased level of prolactin results in an impairment of apolipoprotein biosynthesis and, in addition, in a group with high estradiol level also a lesion of liver function might occur which results in its decreased degradation.