By measuring the electrical conductivity of bathing water solutions, this study examines the post-thaw permeability to electrolytes of suspension-cultered cells freeze-thaw stressed to temperatures in the range from —3 to — 20°C. These permeability measurements are compared to the post-thaw viability of the cells assayed cell-by-cell using vital staining. Supercooling to — 5°C had no effect on permeability or viability by comparison with a + 5°C control, but all freeze-thaw treatments affected permeability based on measurements of electrolyte leakage. This leakage occurred in two stages: (a) an acute stage during thawing which accounted for most of the electrolytes leached (incipient leakage), and (b) a chronic stage in which leakage was relatively slow and declined with time to become comparable to the rate in undamaged control samples. Significantly, this pattern was also found in samples frozen to — 3°C and — 5°C, which killed few cells according to the vital staining assay. It is proposed that the first, acute stage of leakage results from membrane rupture. On the basis of the observations that viable freeze-thawed cells also display incipient leakage, and that chronic leakage is elevated above that of the control, it is tentatively proposed that ruptured membranes subsequently reseal but are transformed with respect to their permeability.