The possible role of lysosomal activity in the early post-trauma phase of severe experimental spinal cord trauma was assessed utilizing an acid phosphatase cytochemical ultrastructural study. The results indicate that there is no evidence for lysosomal alteration prior to the development of cellular degeneration or necrosis. No diffuse cytoplasmic staining was observed. This study indicates that physical lysosomal injury resulting in release of hydrolases into spinal cord cells is not a tenable hypothesis as a primary initiating event in the development of spinal cord necrosis following trauma. However, the data are consistent with the general theory that lysosomal activity is important in the secondary degradation of cells following their being altered beyond recovery.