Infrared spectra were taken for pyridine and its 2- d-, 3- d-, 4- d-, and d 5-homologs in CS 2 solution. All the out-of-plane bands were carefully reassigned. In assigning CH out-of-plane bands their binary combinations played an important part. The least-squares refinement determined a complete, twenty-one constant, quadratic force-field for the out-of-plane vibrations of pyridine, reproducing the forty assigned frequencies with a root-mean-square difference of 2.1 cm −1. Out-of-plane absolute band intensities were measured in CS 2 solution. Comparison between the observed and the calculated band intensities determined the effective charges located on the individual atoms of pyridine. The results for both the force constants and the effective-charge distribution of pyridine were found to be quite reasonable when compared with those of benzene.