An original high-performance liquid chromatographic-mass spectrometric (HPLC-MS) procedure was developed for the determination of cyanide (CN) in whole blood. After the addition of K13C15N as internal standard, blood was placed in a microdiffusion device, the inner well of which was filled with a mixture of taurine (50mM in water)/naphthalene-2,3-dicarboxaldehyde (NDA, 10mM in methanol)/methanol/ concentrated (approximately 20%) ammonia solution (25:25:45:5, v/v). Concentrated H2SO4 was added to the blood sample, and the microdiffusion chamber was sealed. After 30 min of gentle agitation, 2 microL of the contents of the inner vial were pipetted and directly injected onto a NovaPak C18 HPLC column. Separation was performed by a gradient of acetonitrile in 2mM NH4COOH, pH 3.0 buffer (35-80% in 10 min). Detection was done with a Perkin-Elmer Sciex API-100 mass analyzer with an ionspray interface, operated in the negative ionization mode. MS data were collected as either TIC or SIM at m/z (299 + 191) and (301 + 193) for the derivatives formed with CN and 13C15N, respectively. Inspired by previous works dealing with the complexation of CN by NDA + taurine to form a 1-cyano [f] benzoisoindole derivative analyzed by HPLC-fluorimetry, this method appears simple, rapid, and extremely specific. Limits of detection and quantitation for blood CN are 5 and 15 ng/mL, respectively. The use of 13C15N as internal standard allows the quantitation of CN with elegance and accuracy in comparison with previously reported methods.