Amygdaloid stimulations were applied to rats at gradually increasing current intensities once every 60 sec until and afterdischarge (AD) was recorded through the stimulation electrode. These initial AD "thresholds" (x = 75 muA) were reduced over a 4-day period by a series of 12 subthreshold stimulations. In contrast, stimulations administered on the same regimen but at a higher intensity (400 muA) had raised the AD threshold. The decreases in the AD threshold were relatively permanent, whereas the elevated thresholds were subsequently reduced to control levels by a series of subthreshold stimulations or by a 7-day stimulation-free period. Two days following the completion of Experiment 1, all of the rats were injected with a low dose of pentylenetetrazol. The incidence of pentylenetetrazol-induced epileptic symptoms was much higher in the experimental animals than in the control subjects previously subjected only to the threshold estimation procedure.