The analytical method describes the specific determination of 3‐methyl‐5‐isopropylhydantoin (MIH), a hemoglobin adduct of N,N‐dimethylformamide. Following addition of 13C5,15N‐3‐methyl‐5‐isopropylhydantoin (13C5,15N‐MIH) as internal standard, isolated globin is subjected to acid hydrolysis for one hour at 110°C. After pH adjustment (pH 3 – 5) the hydrolysate is extracted twice with ethyl acetate. The combined extracts are washed with sodium hydrogen carbonate solution and dried under a stream of nitrogen. The residue is dissolved in ethyl acetate. An aliquot of the solution is analyzed using GC–MS. For calibration purposes, calibration standards are prepared in pooled globin. They are processed in the same way as the samples to be analyzed.