Serum electrolyte and protein changes in 35 Nigerian patients undergoing intravenous urography were evaluated after injection of 60 mls sodium and meglumine diatrizoate (Urograffin-370). Statistically, significant changes were noted in the values of serum calcium, proteins and albumin at 5 and 30 minutes after the injection (P < 0.005). The mean percentage decreases noted were calcium 13%, protein 17% and albumin 13%. At 30 minutes post-injection, the serum protein and albumin levels had incompletely recovered while calcium values continued to decrease. Non-statistically, significant changes were observed in the values of serum sodium, potassium and phosphate at 5 and 30 minutes respectively following contrast medium injection. Alterations in the levels of serum electrolytes especially calcium are most probably responsible for such adverse effects as convulsions and cardiac arrhythmias.