The FT-IR spectra (7500-1800 cm(-1)) of phenol-OH(OD). pyridine complexes are investigated at 25 degrees C in carbon tetrachloride. The pK(a) of the phenols range from 10.2 to 6, and no proton transfer occurs in the fundamental and first excited vibrational state. The anharmonicities of the nu(OH ... N) and nu(OD ... N) vibrations are determined from the experimental frequencies of the fundamental transitions and of the first overtones. The anharmonicities of the nu(OH ... N) vibration are rather high (between 180 and 235 cm(-1)) and are lower for the nu(OD ... N) vibration (between 115 and 125 cm(-1)). The first overtone of the nu(OH ... N) vibration shows for the stronger phenol-OH pyridine complexes a splitting assigned to proton transfer in the second vibrational excited state. The principal values of the potential shape (barrier height and values of the two minima) are calculated by the Lippincott-Schroeder potential function. The computed parameters indicate that for the weakest complexes the second minimum potential is higher than the upsilon = 2 vibrational level, in contrast with the strongest complexes, where the second minimum occurs at lower values than the upsilon = 2 level. The isotopic ratio varies between 1.346 and 1.255. The lowest values are observed for the complexes where the barrier top is in the vicinity of the first excited vibrational level. The correlation between the enthalpies of complex formation and the experimental and harmonic frequency shifts is discussed. The overtones and combination bands of pyridine are more perturbed in the stronger complexes.