Objective To investigate endometrial endothelin type I (ET-I) level during menstrual cycle and its change after implant insertionMaterials &. Methods It was a prospective control study based on endometrial samples from 27 healthy women using radio-immunity technology. ET-I level in proliferation period and secretion period were measured and compared. ET-I level before and 3 to 7 months after implant insertion were also compared. The side effect of long term use of implant was also study by measuring the ET-I level among women 24 to 36 months after implant insertion.Results ET-I level in proliferation period zvas 2. 76±1. 25 pg/mg, which was sig-nificantly(P<0. 05) lower than that in secretion period (3. 90±1, 30 pg/mg). ET-I level in 14 women , from whom samples before and 3 to 7 months after implant insertion were obtained, were3. 38± 1. 17 pg/mg and 10. 86± 3. 93 pg/mg respectively, with significant statistical difference (P<0. 001). At different periods of implant insertion, the average ET-I leve Objective To investigate endometrial endothelin type I (ET-I) level during menstrual cycle and its change after implant insertion Materials &. Methods It was a prospective control study based on endometrial samples from 27 healthy women using radio-immunity technology. ET-I level in proliferation period and secretion period were measured and compared. ET-I level before and 3 to 7 months after implant insertion were also compared. The side effect of long term use of implant was also study by measuring the ET-I level among women 24 to 36 months after implant insertion. Results ET-I level in proliferation period zvas 2. 76 ± 1. 25 pg / mg, which was sig-nificantly (P <0. 05) lower than that in secretion period , 30 pg / mg) ET-I level in 14 women, from whom samples before and 3 to 7 months after implant insertion were obtained, were 3. 38 ± 1. 17 pg / mg and 10. 86 ± 3. 93 pg / mg respectively, with significant statistical difference (P <0.001). At different periods of implant insertion, the average ET-I leve