Abstract
We present here experimental evidence of the coupling between smectic and nematic ordering in systems exhibiting the reentrant nematic phase. Pressure-temperature diagrams of a large number of systems have been studied. In every case the major axis of the elliptically shaped smectic A-nematic phase boundary is found to be nearly parallel to the nematic-isotropic phase boundary although the slopes vary widely from system to system. Similar correlations are also shown to exist in the temperature-concentration diagram of binary systems. A few representative phase diagrams are presented which illustrate this point.