We have studied a selection of infrared variable stars at wavelength 2.7 μm during 1971-1975 with data from U.S. Air Force satellites. Stars observed in this program are classified as long-period variable stars, semiregular variables, and irregular variables and are among the strongest stellar sources at this wavelength. In addition, a few new, as yet unclassified variable stars were identified during the course of the investigation. Time scales of reproducible variations range from a few weeks to a few years, and amplitudes of variation are as large as a factor of three for stars with periods of order one year. The minimum infrared flux density of a long-period star repeats accurately from one cycle to the next, whereas the maximum flux density was found to be unstable. This behavior may be related to the propagation of shocks in the stellar atmosphere near the time of maximum light or to coupling between large-scale convection and pulsation. It suggests that phenomena in these stars be timed with respect to minimum phase, rather than maximum phase as done previously. Maximum infrared flux density occurs after maximum visible light, whereas the visible and infrared minima are essentially simultaneous. The correlation of 2.7 μm and radio emission line data from one, well-studied long-period variable is consistent with the hypothesis that the H2O and OH circumstellar masers are saturated, if pumped by the stellar infrared flux near 2.7 μm, as suggested by Litvak. However, an alternate model, namely that the radio maser clouds are pumped by long-wave infrared radiation, cannot be excluded.