The rotational spectra of five vibrational states of pyridine have been assigned and measured by millimeter wave absorption spectroscopy in a supersonic expansion. The intensities of the lines of the vibrational satellites with respect to the ground state after the supersonic expansion depend on the kind of carrier gas, backing pressure, pyridine concentration, and symmetry of the rotational and vibrational states. Several rotational transitions of the vibrational satellites have also been measured in a conventional cell to complete the spectral assignment.