The effect of a pulsed electromagnetic field (PEMF) (parameters: 27.1 MHz, 585 W peak power, and 65 μs pulses, 400 times per second) on rats undergoing middle cerebral artery occlusion (MCAo) was investigated. Four groups of eight rats each underwent microsurgical MCAo. Two groups were treated with a PEMF generator for 2 h following the onset of ischaemia and were sacrificed at 4 and 24 h following the MCAo respectively. The other two groups were also sacrificed at the same time intervals. Regional brain sodium, potassium, and calcium tissue contents were determined by atomic spectrophotometry. As distinct from results found in spinal cord contusion, no significant difference between the PEMF-treated groups and the non-treatment groups was found. PEMF treatment did not alter the 300% rise in calcium tissue dry weight content observed at 24 h following MCAo in the infarcted tissue. Regional brain water content was determined by the dry weight method. A regionally inconsistent reduction in brain water content was noted in the PEMF-treated rats.