14 mass spectra of 3-aryl-2-thiohydantoins have been analyzed and seve
ral characteristic ions, like RNCS(+), [M-72](+) and [M-SH](+) were ob
served. It was found that the abundance of [M-SH](+) ion depends mainl
y on the kind and substitution mode of the substituent in tile phenyl
ring.