An attempt was made to correlate optical absorption bands in single magnesiura oxide crystals with point defects known to exist from electron spin resonance observations. Optical measurements in the range of 4000 to 50000 cm/ sup -1/ were made on crystals as received, after heat treatments, after ultraviolet or x-irradiation, and after neutron irradiation, with subsequent heat treatment or irradiation. The goal was the assignment of optical bands as due to impurities in particular valence states, to trapped hole centers, or trapped electron centers. Sorae progress was made by comparison of optical and ESR spectra on the same crystals. The point defect for which the correlation of behavior of the two types of spectra was best was the single hole trapped on an oxygen ion adjacent to a positive ion vacancy. The absorption band which is ascribed to this center occurs at 18500 cm/sup -1/, and is responsible for the fleeting violet color of MgO crystals upon irradiation. While neutron irradiation gives rise to F-certers (electrons trapped at negative ion vacancies) and to visible coloration, no assignment of optical bands with particular electron trapping centers was made. (auth)