Human endometrium and menstrual fluid contain placental protein 10 (PP10). 
Placental protein 10 (PP10), a newly isolated protein from the human placenta, was detected by radioimmunoassay in 10 out of 23 extracts of proliferative and secretory endometrium and in all of the 20 menstrual fluids examined.  The concentrations were higher in the secretory phase, when the tissue PP10 content ranged from less than 0.2 to 1.3 microgram/g of endometrial cytosol protein.  In menstrual fluid, PP10 was found at concentrations of 16 to 270 micrograms/l. In RIA, the dose-response curves of endometrial, menstrual fluid and purified PP10 were parallel.  In gel filtration, the major part of PP10 from the endometrium and menstrual fluid eluted in the same fraction as purified placental PP10.  Our results add another placental protein to the list of placental proteins which also appear in the endometrium.