Protein kinase activities in seminal fluids of normo-, hypo-, and oligozoospermic and vasectomized men were measured using lysine-rich histones and partially dephosphorylated phosvitin as acceptor substrates. There was a significant relationship of histone kinase but not phosvitin kinase activities with the number of spermatozoa originally present in the semen. Histone kinase and phosvitin kinase activities were diminished 88% and 62%, respectively, in vasectomy seminal fluid. The sex accessory gland sources of seminal fluid protein kinase activities not associated with spermatozoa were examined in split ejaculates of vasectomized men. Histone kinase activity was greater in the first fractions, suggesting that the prostate is its predominant contributor; whereas the distribution of phosvitin kinase activity did not indicate any preferential accessory gland source of this enzyme.