The glass-forming regions in the quaternary system GeSbTeSe have been obtained for quenching in air and for a constant cooling rate of 5°C min-1. The boundaries of the glass-forming regions and the thermal behaviour of the samples have been deduced from differential thermal analysis and X-ray diffraction. The results may be compared with some limited determinations of glass-forming ability in TeSe, GeTe, GeTeSe and GeSbSe systems, allowing for the fact that in the present work the experimental parameters for preparing and quenching the melts are identical for all the compositions studied. The formation and stability of glasses is discussed in terms of the obtained glass-forming regions and the observed thermal behaviour in differential thermal analysis measurements. Potential-device quality memory and switching compositions are suggested. © 1979.