Long-period and Mira variables are important stages in the late stellar evolution of low and intermediate mass stars. In fact, they are the main sources of galactic dust production and of a large variety of chemical species originating from their circumstellar shells. A reliable quantitative diagnostic and interpretation of these objects demands both, appropriate theoretical models and specific detailed observations, in particular in the infrared regime. We propose periodic fixed time ISOPHOT observations of long--period variables (LPVs) at different wavelengths in the mid-- and far--infrared range. These measurements will yield informations about the temporal variation of the physical conditions in different spatial regions of the circumstellar dust shells and will allow a comparison with detailed dynamical model calculations. It is the aim of this project to study the wavelength--dependence of certain structures appearing in already observed near--infrared lightcurves and in theoretical lightcurves as well. The data obtained with this investigation, combined with ground-based monitoring, will also allow an interpretation of the long--term behaviour of Miras and LPVs in different wavelength regimes. This proposal is an extension of our Central Program proposal (OBSID: ESEDLMAY, PROPID: VACDSLPV), where only two objects will be observed. However, as these observations are concerned with a very special and short interval of the lightcurves, it is possible that the interesting phases may not be met accurately. Therefore, observations of a larger sample of objects are needed to ensure, that at least some of the objects will be observed during the interesting phases and thus the scientific goal will be reached in full depth.