. The observational material contained in the Warner and Swasey Observatory infrared galactic survey was used to study the longitude distribution of M-type stars. This investigation supports the hypothesis that the stars of type M7 or later form a galactic disk whose density decreases with increasing distance from the galactic center. The earlier M-type stars may also form a disk population, but they show some evidence of clustering. In the vicinity of the sun the number of M stars per million cubic parsecs as determined from this study are: 2 for classes M7 or later, 3 for classes M to M6, and 24 for classes M2 to M4. The distribution in space of stars with class M7 or later was found to agree with that of the total galactic mass in the vicinity of the sun. The giant stars of class M2 or later were shown to comprise only about one-tenth of one per cent of the total mass in the volume of space investigated. The ratio of early to late M-type stars was found to decrease as the longitude of the galactic center is approached.