A method for the determination of cyanide and thiocyanate in blood plasma and red cells of humans was established. It involved high-performance liquid chromatography and fluorometric detection by the Konig reaction. Calibration curves for cyanide and thiocyanate were linear in the range 1-200 pmol and 2-300 pmol, respectively. Clean-up methods for the determination of cyanide and thiocyanate in red cells were also developed. These methods were applied for the determination of cyanide and thiocyanate in the blood of smokers and non-smokers.