In this study, microcalorimetric measurements were carried out on 44 tumorous and non-tumorous tissue samples from organs of the uro-genital tract as well as from the mammae and the colon. The aim of this investigation was to compare the results of the microcalorimetric measurements with those of impulse-cytophotometrical and histological examinations in order to provide evidence of the metabolic activity of tumorous and non-tumorous tissues. The course of the heat output of the tissue samples was measured at one-minute intervals and graphically displayed as a function of time. For the evaluation of the results of the microcalorimetrically measured values, the maxima (P(max)), the mean values (PBAR), and the contour integrals (W) of the microcalorimetric curves were determined. It was found that, without exception, all measured metabolic activity values of tumorous tissue samples were distinctly higher than those of non-tumorous tissue samples from the same organ. We conclude that through a microcalorimetric analysis, it is possible to differentiate between healthy and tumorous tissue samples on the basis of a varyingly higher metabolic activity of the malignant samples.