The toxic effects of metrizamide, a new non-ionic contrast medium, and of meglumine iocarmate (Dimer-X), were investigated after injection into the spinal subarachnoid space of rats. Convulsions were seen in 8 of 11 animals with meglumine iocarmate. No such irritative effects seen with metrizamide. Histologic examiniation of the spinal cord was carried out here 4 months. No changes were seen which could be ascribed to toxic effects of the contrast media.