In order to identify those myelographic risk factors associated with a higher incidence of adverse effects, myelographic technique, patient variables and post-myelographic symptoms were prospectively recorded in a group of 152 patients studied with iopamidol and in a second group of 28 patients studied with iohexol. None of the technical factors studied were identified to have a statistically significant relationship with the incidence of adverse reactions. Older patients fared better than younger patients in both groups. Overall, there was a lower incidence of side effects in the iopamidol group (29%) than in the iohexol group (50%). Headache, nausea, and vomiting were the most frequent reactions seen.