Power-time curves of the growth of a tongue cancer cell line (CP2) and a normal human embryonic lung cell line (Fu(2)P(1)) have been determined by a microcalorimeter at 37 degrees C and 45 degrees C, respectively. The experiments showed that the ratio of the maximal thermal power of both kings of cell growth, P-max (CP2, 37 degrees C/P-max (Fu(2)P(1), 37 degrees C), equalled 1.74 at 37 degrees C, while at 45 degrees C, P-max (CP2, 45 degrees C)/P-max (Fu(2)P(1)), 45 degrees C) = 0.464. The ratio of the metabolic heat for both kinds of cell growing for 63 h at 37 degrees C is, Q (CP2, 37 degrees C)/Q(Fu(2)P(1), 37 degrees C) = 2.295, while at 45 degrees C after both kinds of cells grow for 15 h, Q(CP2, 45 degrees C)/Q(Fu(2)P(1), 45 degrees C) = 0.686. As a comparison, Q(CP2, 37 degrees C)/Q(CP2, 45 degrees C) = 1.734, Q(Fu(2)P(1), 37 degrees C)/Q(Fu(2)P(1), 45 degrees C) = 0.502. The results indicate that the metabolic activity value of the tumor cell is distinctly higher than that of nontumor cell at 37 degrees C, but lower at 45 degrees 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.