High hydrostatic pressure (50 to 500 kg/㎠) was applied to isolated longitudinal muscle strip (10 to 15 mm long, 2 to 3 mm wide) of frog intestine immersed in Ringer's solution containing some drugs, and from the observation of changes of the tonus and rhythmical movement of the preparation following results were obtained. 1) When a drug acts upon the strip during compression, such as magnesium sulfate, barium chloride, acetylcholine or atropine sulfate, the changes on the strip result in algebraic summation of the pressure- and drug-effects. But the action of adrenaline chloride on the strip is reversed under high hydrostatic pressure. Namely, the movement of the strip inhibited by adrenaline or pressure respectively, but it is augumented when the pressure is applied on the strip immersed in the adrenaline-Ringer's solution. 2) The stimulative effect on the muscle strip under high hydrostatic pressure up to 100 kg/㎠ is of neurogenic nature. But under pressure from 300 to 500 kg/㎠ the first instaneous lengthening of the strip and successive slow shortening are observed and this effect is of myogenic nature. 3) The temporary contraction of the strip immediately after decompression may be considered as an adaptive process in biological phenomenon
