By way of comparison the influence of psychostimulators -- benzedrine, caffein and sydnocarb -- on the physical performance capacity of rats exposed to heat and cold was studied. It was ascertained that psychostimulators are capable of heightening the performance capacity of the animals, viz. benzedrine in cooling -- in a dose of 1 mg/kg; caffein -- in overheating -- in a dose of 30 mg/kg; sydrocarb -- in overheating -- in a dose of 5 mg/kg. In the case of benzedrine the increase of performance capacity reaches 29.4, in that of caffein -- 21.0 and in sydnocarb -- 42.1 per cent above the initial level.