A method for assessing the mitochondrial toxicity of a candidate compound, the method comprising a) exposing one or more 3-dimensional cell culture or tissue to one or more candidate compounds, and b) measuring, in at least one 3-dimensional cell culture or tissue, the effect of such exposure on the specific respiration rate of the 3-dimensional cell culture or tissue (microtissue-specific respiration rate, MTSRR), c) measuring, in the same or at least one other 3-dimensional cell culture or tissue, the effect of such exposure on cell viability and/or the cytotoxic effect (CV-CYT) in one or more cells of at least one 3-dimensional cell culture or tissue, and d) comparing the effects of steps b) and c) to provide an estimate on the mitochondrial toxicity of the one or more candidate compounds, wherein the mitochondrial toxicity is determined on the basis of the quantitative relationship between I) the IC 50 with respect to the specific respiration rate of the 3-dimensional cell culture or tissue (IC 5O-MTSRR ) II) the IC 50 with respect to the cell viability/cytotoxicity (IC 5O-CV/CYT ), wherein (i) IC 5O_MTSRR ≥ IC 5O_CV/CYT means that the candidate compound has no specific mitochondrial toxicity (ii) IC 5O-MTSRR < IC 5O_CV/CYT and IC 5O-MTSRR ≥ 0.75 x IC 5O_CV/CYT means that the candidate compound has a low risk of mitochondrial toxicity (iii) IC 5O-MTSRR < 0.75 x IC 5O_CV/CYT means that the candidate compound has a high risk of mitochondrial toxicity. a) exposing one or more 3-dimensional cell culture or tissue to one or more candidate compounds, and b) measuring, in at least one 3-dimensional cell culture or tissue, the effect of such exposure on the specific respiration rate of the 3-dimensional cell culture or tissue (microtissue-specific respiration rate, MTSRR), c) measuring, in the same or at least one other 3-dimensional cell culture or tissue, the effect of such exposure on cell viability and/or the cytotoxic effect (CV-CYT) in one or more cells of at least one 3-dimensional cell culture or tissue, and d) comparing the effects of steps b) and c) to provide an estimate on the mitochondrial toxicity of the one or more candidate compounds, wherein the mitochondrial toxicity is determined on the basis of the quantitative relationship between I) the IC 50 with respect to the specific respiration rate of the 3-dimensional cell culture or tissue (IC 5O-MTSRR ) II) the IC 50 with respect to the cell viability/cytotoxicity (IC 5O-CV/CYT ), wherein (i) IC 5O_MTSRR ≥ IC 5O_CV/CYT means that the candidate compound has no specific mitochondrial toxicity (ii) IC 5O-MTSRR < IC 5O_CV/CYT and IC 5O-MTSRR ≥ 0.75 x IC 5O_CV/CYT means that the candidate compound has a low risk of mitochondrial toxicity (iii) IC 5O-MTSRR < 0.75 x IC 5O_CV/CYT means that the candidate compound has a high risk of mitochondrial toxicity. I) the IC 50 with respect to the specific respiration rate of the 3-dimensional cell culture or tissue (IC 5O-MTSRR ) II) the IC 50 with respect to the cell viability/cytotoxicity (IC 5O-CV/CYT ), wherein (i) IC 5O_MTSRR ≥ IC 5O_CV/CYT means that the candidate compound has no specific mitochondrial toxicity (ii) IC 5O-MTSRR < IC 5O_CV/CYT and IC 5O-MTSRR ≥ 0.75 x IC 5O_CV/CYT means that the candidate compound has a low risk of mitochondrial toxicity (iii) IC 5O-MTSRR < 0.75 x IC 5O_CV/CYT means that the candidate compound has a high risk of mitochondrial toxicity. (i) IC 5O_MTSRR ≥ IC 5O_CV/CYT means that the candidate compound has no specific mitochondrial toxicity (ii) IC 5O-MTSRR < IC 5O_CV/CYT and IC 5O-MTSRR ≥ 0.75 x IC 5O_CV/CYT means that the candidate compound has a low risk of mitochondrial toxicity (iii) IC 5O-MTSRR < 0.75 x IC 5O_CV/CYT means that the candidate compound has a high risk of mitochondrial toxicity. <EOS>