Endogenous digoxin-like immunoreactivity (EDLI) has been detected in different biological fluids and in several pathophysiological conditions. In this study, using radioimmunoassay we reported for the first time the existence of bound and unbound EDLI in normal seminal fluid. The unusual finding was the detection of unbound EDLI in the seminal fluid, while this reactivity was undetected in plasma. Two main hypotheses are presented: (1) local secretion of unbound EDLI and/or (2) passive diffusion from plasma to the seminal fluid of unbound EDLI and subsequent local concentration.