Treatment of endometriosis with antileukoprotease

There is disclosed a method of measuring an amount of antileukoprotease in an endometrial tissue sample which has been obtained from a human subject, which comprises measuring an amount of antileukoprotease activity or antileukoprotease mRNA, in an endometrial tissue sample which has been obtained from a subject, wherein the amount of antileukoprotease in the sample is measured as a function of the amount of antileukoprotease activity or antileukoprotease mRNA , in the sample. There is also disclosed the use of a compound that inhibits the activity of antileukoprotease for the manufacture of a medicament to facilitate the implantation of an embryo in the uterus of a subject, wherein the compound is administered in early pregnancy or before conception.