Purified human seminal plasma acid phosphatase is inhibited by sodium fluoride and L(+) tartrate and 50% inhibitions (I50) have been obtained at 7.3 X 10(-5) and 3.0 X 10(-4) M concentrations, respectively. By Lineweaver-Burk plot, sodium fluoride shows non-competitive type of inhibition. Ackermann plot indicates that sodium fluoride is a reversible inhibitor of seminal plasma acid phosphatase. On polyacrylamide activity gel electrophoresis and by densitometric scan, a single molecular form of acid phosphatase has been identified in human seminal plasma. Inhibition patterns by sodium fluoride and L(+) tartrate have also been performed by polyacrylamide activity gel electrophoresis and almost complete inhibition of hydrolysis of alpha-napthol phosphate is observed at 20 mM and 100 mM of sodium fluoride and L(+) tartrate, respectively.