Purpose: It is currently believed that cancer procoagulant (CP), an enzymatic protein, is a product of malignant neoplastic cells. The present study was designed to test whether it is also synthesized by benign neoplastic cells, namely uterine leiomyomas. Materials and methods: We determined the activity of CP in the blood serum of women with uterine leiomyomas (N = 24), normal women (N = 15), and genital cancer patients (N = 6) by the coagulative method according to Gordon and Benson. Also, the CP activity in 10% tissue homogenates of uterine leiomyomas, normal uterine muscle and tissues of cervical and endometrial carcinoma was determined by the chromogenic method according to Colucci et al. Results: The mean CP activity in the sera of women with uterine leiomyomas was 181.1 seconds (s) ± 19.9 s, in healthy women - 293.2 s ± 33.8 s, and in genital cancer patients - 78.8 ± 18.5 s (all differences: p < 0.001). Similarly, in homogenates of uterine leiomyomas the CP activity was 19.6 ± 3.8 nmoles pN小ml, in normal uterine muscle it was 13.2 ± 2.2 nmoles pNa/ml, and in can­cerous tissue - 28.0 ± 6.6 nmol pNa/ml (all values being significantly different from each other). There was a strong correlation (r = -0.8122; p < 0.001) between the CP activity in uterine leiomyomas and serum activity, suggesting that the source of the serum CP activity was from the leiomyoma. The coagulation time of 120 to 240 s by the Gordon and Benson method supported the diag­nosis of uterine leiomyoma, and a value below 120 s - the suspicion of genital cancer. Conclusions: Uterine leiomyomas, representing benign genital neoplasia, synthesize CP and are the likely origin of CP activity in blood, as has been described for malignant tumors, but to a lesser degree. There may be a role for CP as a tumor marker of genital neoplasia.