Prussian blue salts are used in clinical practice as an antidote for the treatment of humans contaminated with radioactive cesium. A decomposition product of these Prussian blue salts may be the highly toxic cyanide. A method to simulate gastrointestinal cyanide-release was applied to four different Prussian blue salts: K3Fe[Fe(CN)6], Fe4[Fe(CN)6]3, NH4Fe[Fe(CN)6] (pur. and unpur.). Cyanide-release was higher in artificial gastric juice than in water and artificial intestinal juice. Under all conditions cyanide-release from Fe4[Fe(CN)6]3 was the lowest. Since Fe4[Fe(CN)6]3 also binds more cesium, it appears to be the most suitable Prussian blue salt for use as an antidote after radiocesium contamination in humans.