In order to investigate the effects of slowly increasing localized cortical pressure on the electroencephalogram (EEG), a series of 40 rabbits was studied by a specially designed apparatus devised to record the electrical waves and at the same time produce a localized brain compression. The combination compression apparatus and electrode consisted of a lucite rod 0.713 cm. in diam., and 3.81 cm. long. Extending through this rod were 2 silver wires which barely protruded at the distal end to make direct contact against the dura. The rod was attached to a micrometer screw. One com-plete revolution moved the rod 0.079 cm. Slowly increasing localized cortical pressure produced the following abnormalities in the EEG pattern (a) seizure patterns; (b) associated seizure patterns consisting of fast and slow waves, as well as spikes; (c) delta or slow waves, below 5 cycles/sec; (d) combination wave patterns consisting of fast waves superimposed on delta waves; (e) flat waves wherein the voltage was reduced to below 20 uV. The seizure, and associated seizure patterns, showed involvement of all three electrodes in 47.5%. The seizure, and associated seizure patterns, were definitely localized to the pressure electrode in 42.5%. 95% of the seizure, and associated seizure patterns, involved the pressure electrode. During a paroxysm, single or multiple patterns were observed. The incidence of seizure patterns occurred more frequently during compression than during release. The delta waves, flat waves and combination waves were primarily confined to the pressure electrode. Delta voltage increased during compression until approx. the 4th turn, then the voltage decreased. During release, the delta voltage slowly increased. The incidence of flat waves increased in direct relation to the degree of compression. The incidence of combination waves slowly increased until the 6th turn of compression, then decreased. Combination waves were absent during the release stage.