Power-time curves of the growth of a tongue cancer cell line (CP 2 ) and a normal human embryonic lung cell line (Fu 2 P 1 ) have been determined by a microcalorimeter at 37°C and 45°C, respectively. The experiments showed that the ratio of the maximal thermal power of both kinds of cell growth, P m a x (CP 2 , 37°C)/P m a x (Fu 2 P 1 , 37°C), equalled 1.74 at 37°C, while at 45°C, P m a x (CP 2 , 45°C)/P m a x (Fu 2 P 1 ), 45°C) = 0.464. The ratio of the metabolic heat for both kinds of cell growing for 63 h at 37°C is, Q (CP 2 , 37°C)/Q(Fu 2 P 1 , 37°C) = 2.295, while at 45°C after both kinds of cells grow for 15 h, Q(CP 2 , 45°C)/Q(Fu 2 P 1 , 45°C) = 0.686. As a comparison, Q(CP 2 , 37°C)/Q(CP 2 , 45°C) = 1.734, Q(Fu 2 P 1 , 37°C)/Q(Fu 2 P 1 , 45°C) = 0.502. The results indicate that the metabolic activity value of the tumor cell is distinctly higher than that of non-tumor cell at 37°C, but lower at 45°C. By means of microcalorimetry, it is demonstrated that temperature has a remarkably selective destructuring effect of heat against tumor cell. The results of 6 other kinds of cancer cells and normal cells at different temperatures are also in agreement with the results obtained. Also, the power-time curves of the two passages of the tongue cancer cell (P 6 and P 7 ) are determined. The difference between the two passages is shown clearly on the power-time curves. It is concluded that microcalorimetry could be used as a powerful tool to characterize the passages of the cell.