Role of serum prolactin determination in evaluation of impotent patient. Hyperprolactinemia is a recognized cause of impotence. The discovery of elevated prolactin levels in impotent men is very important since pharmacotherapy in this instance is highly successful. We review our experience with prolactin determinations in impotent men, and a population is defined that may benefit from routine prolactin determination. In our experience, the predominant symptom associated with hyperprolactinemia in men is loss of libido. 