Sodium nitroprusside (SNP) is an effective vasodilator but is potentially dangerous due to its cyanide content. Infusion rates above 2 micrograms/kg/minute may cause cyanide to accumulate to toxic concentrations in critically ill patients. Coadministration of thiosulfate with SNP effectively and safely prevents cyanide toxicity. This study determined if patients at our institution were treated with SNP infusion rates that could cause cyanide toxicity and whether those patients were administered thiosulfate. We reviewed the charts of 36 critically ill patients treated with SNP during the previous 12 months. In 72% of patients the SNP infusion rates were above 2 micrograms/kg/minute. In 47% the rates were greater than 2 micrograms/kg/minute for 6 hours or more, and in 20% they were greater than 5 micrograms/kg/minute for up to 11 hours. None of the patients was administered thiosulfate. In a significant number of patients the infusion rates of SNP potentially exposed them to significant risk of cyanide toxicity including death.