Ornithine decarboxylase (ODC) activity in human breast cancer tissues was correlated with prolactinemia (Prl), estradiol and progesterone cytosol receptors (ER and PR), and histopathologic pattern. Ninety-two cases of breast cancer, six benign mammary disease, and three normal breast tissues were studied for ER, PR, and ODC. Prolactinemia was assessed in 59 cancer patients, 14 of whom showed hyper-Prl along with significantly higher O X than in patients with normal-Prl I(20.01 & 6.33) lo-' YS (5.20 k 0.90) lo-* pmol C02/pg protein/& P < 0.01251. A direct correlation was found between Prl and ODC in postmenopausal women (n = 40). Prl was assayed in seven of 13 ER-PR breast cancer patients; a highly significant, direct correlation was found between Prl and ODC in this group (r = 0.934, P