lSN NMR spectra of a number of 2-mercaptoazoles were obtained and the position of the iminothiol-thioamide prototropic tautomeric equilibrium was determined. Because of the large chemical shift difference of cu 100 ppm between the iminothiol and thioamide nitrogen atoms, the I5N chemical shifts of the S-methyl and N-methyl analogs of each tautomer provided reasonable chemical shift models for the same nitrogen atom in the tantomers. Only a small correction for an N-methyl effect was required.