Ethylenebisisothiocyanate sulfide (EBIS) was administered in the diet to groups of rats at 0, 1, 10, 100, and 1,000 ppm for up to 90 days. The rats receiving EBIS at 1,000 ppm demonstrated a toxic response within 8–14 days, reflected as a reversible paralysis of the hind legs. If left on the 1,000 ppm diet, the animals soon died. When removed from the diet, the animals recovered, only to become atoxic on further dietary exposure at the high level. No histologic lesion could be identified in either H&E‐ or luxol fast blue‐stained sections of brain, spinal cord, or peripheral nerves from the paralyzed animals. The ability to reverse the paralysis by removing the animals from the test diet coupled with the lack of histologically observable lesions suggests a biochemical (reversible) rather than somatic lesion.