The B1-antivitamin activity of oxythiamine disulphide nicotinate has been determined in experiments on albino mice and it is shown that in the liver this derivative exerts the equal action while in the blood and heart--a more profound and prolonged inhibitory action on the transketolase activity in comparison with oxythiamine disulphide. Like the initial compound oxythiamine disulphide nicotinate does not penetrate through hemato-encephalic barrier and does not inhibit the brain transketolase.