The amount of ~3H-TdR incorporation into D?A of FRTL5 cells was expressed as CPM/?gD?A. THe responsibity of FRTL5 cells to stimulators such as TSH was expressed as % against thJ control CPM/?gDNA of the experimental group divided by that of the control. The responsibilities of FRTL5 cells which were recovered after being fr-o zen under-180℃ for a long time, to TSH 200?g/ml were 2741% and 3028% respectively, and the responsibilities of cells cultured in TSH media continuously for a long time, to TSH 200?u/ml and 2000?u/ml were 736% and 719% respectively. There was statistically significant differences between the two groups of the cells mentioned above. This showed that freezing FRTL5 Cells for a long time Such as 2 months was able to recover the decreased responsibility of the Cells due to a long continuous TSH culture.