High hydrostatic pressure (500 kg/㎠ and 1,000 kg/㎠) was applied to an enucleated eyeball and eyeballs of the decapitated frog head, which were suspended in Ringer's solution. Next, some autonomic drugs were added to the solution to make them act on the eyeballs before, during or after compession. By observing the pupillary changes, the following results were obtained. 1) After decompression the pupil becomes wide at first and then narrow. But the miosis after decompression does not occur in the same manner in the enucleated eye as with those of the decapitated head. 2) The effects of autonomic drugs also vary according to the difference whether the eye has connection with the central nervous system or not. 3) These facts appear to prove that high hydrostatic pressure has marked influence on the central nervous system. Its sensitivity to autonomic drugs is remarkably raised by high pressure.