The exact low-temperature series-expansion formalism of spin-89 anisotropic Ising two-sublattice antiferromagnets will be discussed in their parallel magnetic field configuration. In terms of reduced temperature and reduced .field strength, defined through the molecular-field spin-ordering transition temperature and the associated critical magnetic field strength of the system, at asymptotically low temperatures, the various thermal properties are expressed through a few exponential terms. At large values of a unique dependent variable of the theory and in leading order the exact formalism is identical with that of molecular-field theory of the above systems. The entropy at constant field strength, approaching critical strength, remains very large down to quite low temperatures. As a consequence, in eventual real systems of low transition temperature which behave predominantly as Ising antiferromagnets or which closely simulate the latter, adiabatic magnetization up to the neighborhood of the critical field strength should produce substantial cooling, provided certain possible competing nuclear warming effects remain reasonably small. The heat capacity at constant applied field strength, approaching critical strength, develops a low-temperature maximum in addition to its transition anomaly along the antiferromagnetic-paramagnetic phase boundary line. This exact result, found earlier in, and attributed to, the approximate molecular-field theory, might be useful for experimentally identifying the presence or absence of dominant Ising-like interactions in certain eventual real anisotropic antiferromagnets.