Sixteen anesthetized dogs undertook a chamber dive that was designed to induce decompression sickness. Somatosensory evoked potentials (SEP) were used to diagnose and quantify the outcome of spinal cord involvement in the disease. Following diagnosis, 8 animals were treated with methyl prednisolone (MP), 20 mg.kg-1 ("megadose"), as an adjuvant to recompression on an abbreviated U.S. Navy Treatment Table 6. Eight control animals were recompressed in a similar manner, but received the MP diluent only as an adjuvant. Analysis of the SEP at the conclusion of treatment showed that there was no significant difference in outcome for the 2 groups of animals. However, if all the SEP recorded during the treatment period are compared, the MP-treated animals experienced a significantly worse outcome than the diluent-treated controls. The risks and benefit of using corticosteroids in the treatment of human spinal cord DCS are discussed.