The present method allows for the determination of the main metabolites of N,N‐dimethylformamide and N,N‐dimethylacetamide in urine: HMMF, NMF, HMMA and NMA, respectively. HMMF and HMMA readily decompose thermally to form N‐methylformamide (NMF) or N‐methylacetamide (NMA) and formaldehyde. Prior to sample injection, thermolysis is carried out for 2 hours at 120°C in order to transform the metabolites completely into the target analytes NMF and NMA. The urine samples are then diluted with ethanol and analyzed using GC–MS. Thus, the sum of HMMF and NMF (DMF metabolites) and the sum of HMMA and NMA (DMA metabolites), respectively, are detected by this procedure.