Abstract
In metals at ultra-high compressions, pressure ionization of the cores takes place. The highest hydrostatic pressures so far attained (600 kbar) appear to be in or approaching this regime in the cases of K, Rb and Cs. A simple model for ionized cores leads us to predict order-of-magnitude increases in resistances above those at zero pressure. These are in agreement with the asymptotic behaviour of the observed curves for Rb and Cs and with that suggested by the observed curve for K.