Cyanamide (NH2CN) is found in nature, although it has long been recognized as an industrial product. Distribution of cyanamide in the plant kingdom was investigated using a direct quantitative determination method to detect and measure cyanamide by stable isotope dilution gas chromatography-mass spectrometry (the SID-GC-MS method). The SID-GC-MS method proved to be a robust way to quantify cyanamide contents in the extracts of 101 species of herbaceous plants. The average recovery of cyanamide from all plants tested was 55.6+/-20.3%. Vicia villosa and V. cracca contained cyanamide at 369-498 microg/gFW and 3,460-3,579 microg/gFW respectively, while the other 99 species contained no detectable cyanamide (<1 microg/gFW). This result suggests that distribution of cyanamide in the plant kingdom is limited and uneven.