Activation of arachidonic acid occurs after spinal cord injury. Leukotriene B4 is a lipoxygenase metabolite of arachidonic acid. In a rat model of experimental spinal cord injury, we found that the leukotriene B4 content was less than the sensitivity of our assay (8 pg/mg of protein) in non-traumatized spinal cord. Leukotriene B4 was detectable in traumatized cord (mean +/- SE, 25 +/- 5 pg/mg of protein; n = 3). Release of leukotriene B4 from spinal cord slices into the incubation medium was also noted after trauma (9 +/- 1 pg/mg of protein; n = 12) and was enhanced by exposure of traumatized spinal cord slices to the calcium ionophore A23187 (375 +/- 43 pg/mg of protein; n = 12). The amount of leukotriene B4 released corresponded to the extent of post-traumatic polymorphonuclear cell infiltration determined by a myeloperoxidase assay. Results from this study suggest that the source of leukotriene B4 in spinal cord injury is infiltrating polymorphonuclear cells.