Separation of isoforms of angiotensin I converting enzyme (EC 3.4.15.1, ACE) from human semen was attempted by chromatographic procedures. The crude ACE was fractionated on DEAE-Sephadex A-25 and Sephadex G-200 columns. Two ACE components were separated out in the first DEAE-SEphadex A-25 chromatography. The two ACE preparations (S-I and S-II) were separately applied to gel filtration through a Sephadex G-200 column. S-I was further separated into two peaks. Elution of the first peak showed MW about 150KD, while the second peak corresponded to MW about 100KD. S-II was eluted as a single Peak at an elution position corresponding to MW about 150 KD. At least three ACE components were separated out from the seminal extract.