Objective: To observe the clinical effect of Neiyifang (NYF) in treating endometriosis and to explore its therapeutic mechanism through observing its influence on plasma β-endorphin (β-EP) in different menstrual stages and levels of prostaglandins (PGs) in menstruation.Methods:NYF was administered to 104 patients with endometriosis one dose daily with 3 successive menstrual cycles as one therapeutic course. Peripheral blood β-EP level in follicular

luteal and menstrual stages

as well as PGF2α

PGE2

thromboxane B2 and 6-keto-PGFl α levels in menstrual stage were detected by RIA

and controlled with those in 15 healthy persons.Results: (1) The total effective rate of NYF was 81.3% and it showed significant effect in improving patients’ clinical symptoms and physical signs; (2) In menstrual stage

the levels of β-EP

6-keto-PGFα/ TXB2 were lower(P <0.05) and levels of PGF2α

PGE2

TXB2 and 6-keto-PGF1α were higher (P< 0. 05) in patients than those in control

and the higher the level of PGE2

the severer the menalgia

(3) NYF could increase levels of β-EP

6-keto-PGF1α

and reduce levels of PGF2α

PGE2α in menstrual stage of patients (all P<0.05).Conclusion: (1) NYF has good clinical effect in treating endometriosis; (2) Patients’ symptom of menalgia is closely related with the excessive high levels of PGF2α and PGE2

PGI2/TXA2 ratio disturbance

and excessive low level of β-EP; (3) NYF could significantly decrease the PGE2

PGF1α levels

increase the 6-keto-PGF1α/TXB2 ratio and the level of β-EP

so as to alleviate the menalgia in patients with endometriosis.