The concentration of cyanide, a toxic metabolite of sodium nitroprusside, in solutions other than 5% dextrose in water, has not been reported. In this study, cyanide ion levels were measured by a cyanide ion-specific electrode in 250 ml of six different intravenous solutions (5% dextrose in water, 10% dextrose in water, distilled water, 0.9% sodium chloride, and lactated Ringer's solution with and without 5% dextrose) exposed to 300 foot candles of fluorescent light for 72 hours after sodium nitroprusside was dissolved in each solution. The rates of the increase in cyanide ion concentration in all six solutions were fairly constant between 4 and 24 hours. At 24 hours, there were no statistically significant differences in cyanide ion concentration among the six solutions. After 24 hours, the rate of the increase in cyanide ion concentration in the electrolyte solutions decreased more than that in the nonelectrolyte solutions. At 72 hours, the electrolyte-containing solutions had statistically significant lower mean cyanide ion concentrations than 5% dextrose, often the recommended diluent for sodium nitroprusside. There was no difference in mean cyanide ion concentration between lactated Ringer's solution with and without 5% dextrose. Solutions containing electrolytes are preferable to 5% dextrose for the dilution of sodium nitroprusside.