The concentration of human protein factor of fertility (PFF) in seminal plasma was measured by a semi-quantitative immunodiffusion method with the standard test system. Fresh seminal plasma from 202 men with normal fertility was investigated. The levels of PFF ranged from 2 to 512 mg/l in normospermic specimens. The retrospective analysis revealed a positive correlation (p < 0.001) between low PFF concentration (2–8 mg/l) in the husband’s seminal plasma and primary early spontaneous abortion in the wife.