This paper deals with experimental studies on the polarization IR spectra of hydrogen bonds in 2-mercaptothiazoline and 2-mercapto-1-methylimidazole crystals. The crystal structure of 2-mercaptothiazoline was determined by X-ray diffraction. The polarization spectra of the two compounds were measured in the frequency ranges of the V(N-H) and V(N-D) bands at 77 and 298 K. The spectra were attributed to cyclic N-H...S hydrogen-bond dimers, which are present as structural units in the lattices. Variation of the Davydov-splitting energy magnitude from sample to sample suggests statistical disorder in the crystals. The influence of the electronic properties of the associating small-ring molecules on the spectral properties of the hydrogen bonds is also discussed.