Hepatopoietin (HPO) has diverse functions in the regulation of cell growth and differentiation. Its high level expression in testis suggests that HPO may have important role for testicular physiological functions. Using HPO as “bait”, a yeast two-hybrid library screen of human testis was performed. By screening and selecting the positive colonies, retesting interactions in yeast, amplifying the AD/library inserts, sequencing and sequence comparing, four HPO-interacting proteins were identified: NADH dehydrogenase 1, Na⁺/K⁺ ATPase beta-3 subunit (ATP1β3), phospholipase C delta 1 and epididymal secretory protein. The significance of identification of these proteins may provide mechanistic insight into the biologic role of HPO in testis.