The spectra of 10 interstellar OH maser complexes were monitored in the 1665 MHz transition for variability on short (minutes-hours) and long (days-years) time scales. Eight of the sources exhibit short time scale variability in the relative amplitudes of the spectral features above that expected due to radiometer noise, and all sources for which multiepoch observations were made show variability on long time scales. Amplitudes of the short time scale fluctuations are typically 5-10 percent of the peak intensity and are as large as 20 percent. Over long time scale, the fluctuations range from 0 to nearly 100 percent in amplitude. The OH emission spectrum from a main-line OH/IR star was also monitored. Long time scale variability is noted, distinct from that caused by pulsations of the stellar pumping source, while no short time scale variability (above 5 percent) is apparent. 46 refs.