Failure to mix 24.5 mM of magnesium, added as 50% MgSO4 in 1 liter of intravenous fluid, results in a high concentration of Mg in the initial 10-cc aliquot: 1,145.7 mM/liter. Adequate dispersion can be obtained after three inversions. We conclude that because of the extremely high concentrations of Mg that can result if no mixing is done, it is imperative that hospital personnel ensure that added Mg is adequately dispersed in intravenous fluid prior to administration. A method of signalling the inadequacy of mixing is to color code additives with a harmless dye to alert personnel to the problem of inadequate dispersement.