Several studies are summarized in which the relationship of high prolactin levels and self-rated anger-hostility was examined. The Symptom Questionnaire, a state measure which contains an anger-hostility scale, was included in all studies. Women with hyperprolactinemic amenorrhea were found to have higher hostility scores than amenorrheic women with normal prolactin levels. In another study, hyperprolactinemic women were found to have higher hostility scores than female family practice patients, random employees and there was a nonsignificant trend for higher hostility scores than in female nonpsychotic psychiatric outpatients. In both studies, depression and anxiety were also significantly higher. When bromocriptine, a prolactin lowering drug, was administered to hyperprolactinemic women in a double blind crossover study, there was a significant and progressive decrease of hostility, depression and anxiety while on bromocriptine, parallel with the decrease in prolactin and no change on placebo. Post-partum women who had high prolactin levels were significantly more hostile than a control group of employees and as hostile as hyperprolactinemic women. Hyperprolactinemic males were no more hostile than controls. The relationship of prolactin to post-partum aggression in mammals is briefly reviewed. The findings are inconclusive; in the three species studied, postpartum aggression is perhaps enhanced, but does not depend on high prolactin levels. There are no studies on the relationship of prolactin levels and violence in women. Hostility associated with high prolactin levels in postpartum women is perhaps a phylogenetic remnant which may have had the evolutionary advantage of protecting the young.