The amount of hydrazine compounds, calculated as gyromitrin (N-methyl-N-formyl hydrazone of acetaldehyde) remaining in false morels during drying and cooking processes was followed. Boiling of false morels in a large amount of water for 10 minutes, the usual household procedure, destroys an average of 99.5% of the hydrazines. The amount of hydrazines in dried false samples was not constant: the 99-100% of the original amount was lost during the drying process. The mass, infra-red, 1H NMR and 13C NMR spectra of synthetic gyromitrin were recorded. The NMR spectra were analyzed with double resonance methods.