Human kallikrein 10 (hK10), a serine protease, plays an important role in the regulation of cell proliferation and tumor growth. Its presence was demonstrated in lactotrophs and corticotrophs of the nontumorous human pituitary. In this work, we investigated hK10 immunoexpression in 59 surgically removed human pituitary tumors. Tissues were fixed in formalin, embedded in paraffin. Immunostaining was performed by the streptavidin‐biotin‐peroxidase complex protocol using the LSAB+ Kit (DAKO, Carpenteria, CA) and an hK10‐specific rabbit polyclonal antibody (1:150). Results showed that lactotroph adenomas removed from patients receiving no dopamine agonist medication were conclusively immunopositive for hK10. Immunopositivity was localized in the cytoplasm and was clearly visible in many adenoma cells. In the various tumor types (silent corticotroph subtype 1 & 2, oncocytic and gonadotrophic adenomas, somatotroph adenomas, and carcinomas), immunopositivity was very mild, seen only in few unevenly distributed tumor cells. Previous studies showed that hK10 possesses tumor suppressing properties and is decreased in rapidly growing tumor cells. Future studies should focus on hK10 immunoexpression in lactotroph adenomas exposed to dopamine agonist therapy which inhibits tumor growth. This study was supported by the Jarislowsky and Lloyd Carr‐Harris Foundations.