BACKGROUND To investigate the in-vivo effects of intravenous administration of sodium meglumine diatrizoate on some haematological parameters in a Nigerian population. METHODS Blood samples were collected before and one hour after intravenous injection of sodium-meglumine diatrizoate from 50 subjects undergoing intravenous urography examinations who had no history of and laboratory confirmed diseases that may affect haematological parameters. Standard laboratory methods were used to assay the haemoglobin concentration (Hb), packed cell volume (PCV), total white blood cell (WBC) count and differentials and blood film for any morphological changes in the red blood cells (RBC). Comparisons were made between the mean values of these haematological parameters before and one hour post injection using paired t-test for any statistically significant differences. RESULTS There were statistically significant reductions in the mean values of Hb concentration and the neutrophil count one hour post injection compared with their pretest values (p < 0.05). The lymphocytes were also significantly increased post injection compared to the pretest values whereas 70% of the erythrocytes were morphologically altered from their approximately 100% normocytic shape at pre-test. CONCLUSIONS Intravenous administration of sodium-meglumine diatrizoate causes in-vivo reduction in Hb concentration and neutrophil count in humans as well as poikilocytosis of the erythrocytes. Some of these effects have the potential of triggering or exacerbating crisis in a sickle cell anaemia subject which is endemic in our locality. Caution should therefore be exercised in the choice and administration of radiological contrast agents to sickle cell subjects. Preparations that are iso-osmolar with plasma and have less probability in precipitating crises should be preferred instead.