Background: Uterine leiomyomas are benign tumors arising from the myometrial compartment of the uterus. They are the most common gynecologic neoplasm, occurring with a remarkable frequency in more than 70% of women at their reproductive age. The female reproductive tract is known to be an extrapituitary source of the hormone prolactin. Prolactin (PRL) is a polypeptide hormone of growth hormone/cytokine family. In serum, PRL occurs in various molecular forms with different molecular weights, including the physiologically active monomeric form called the little PRL, the big PRL, and the big big PRL, that is also called macroprolactin. Objectives: To study the PRL profiles with its molecular weights in patient’s serum, leiomyomas, and myometrium compared with the PRL profiles of a normal myometrium. Subjects and methods: Circulating prolactin of patient group (n=57) as well as their tissues prolactin [(leiomyomas and myometrium)] and [normal myometrium] of the control group (n=45) was assayed using the Prolactin Kit (Biomérieux). Prolactin profile was detected using the polyethylene glycol 8000 precipitating method to separate the big big prolactin from the monomeric and the big prolactin isoforms. Disk gel electrophoresis technique was used to confirm the prolactin isoforms and to calculate their molecular weights. Results: A highly significant difference was found between the leiomyoma prolactin and patient's myometrium prolactin as well as between the leiomyoma prolactin and the normal myometrium prolactin (P<0.0001), while no significance was found between patient’s myometrium and the normal myometrium prolactin. Also a high significance (P<0.0001) was found between the patients serum prolactin and their leiomyoma prolactin, leiomyoma size, while a significant value (P<0.05) was found between leiomyoma prolactin and their sizes. In this study the prolactin isoforms in patient’s serum, leiomyoma and myometrium as well as in the normal myometrium of control group were monomeric and big prolactin with different molecular weights. Only one sample of patient’s serum had big big prolactin isoform.Conclusion: Serum prolactin level was increased in patient with uterine leiomyoma with a significant positive correlation with the leiomyoma size and its prolactin produced from it. Hyperprolactinemia may be also caused by macroprolactin in patients with uterine leiomyoma because the big forms of PRL have a decreased bioactivity, they do not cause clinical symptoms of hyperprolactinemia.