Introduction. In vitro studies on a culture of cardiomyocytes have shown that dose-response relationships could be monotonic for some effects and non-monotonic for others. In this work, we wanted to demonstrate that these features of the dose-response relationship are a general pattern. Materials and methods. In vitro experiments were conducted on the culture of human fibroblast-like cells FLECH-104. The cytotoxicity of spherical nanoparticles of selenium oxide (SeO-NP) and copper oxide (CuO-NP) was studied with an average diameter of 51 ± 14 nm and 21 ± 4 nm, respectively. Results. SeO-NP and CuO-NP were cytotoxic for human fibroblast-like cells, as judged by a decrease in ATP-dependent luminescence. In this case, the cytotoxicity of CuO-NP was somewhat more substantial than the SeO-NP one. Our experiment revealed doses that cause both cell hypertrophy and a decrease in the size of cells and nuclei. Discussion. We observed both monotonic and different variants of the non-monotonic dose-response relationship. For the latter, it was possible to construct adequate mathematical expressions based on the generalized hormesis paradigm that we had considered earlier concerning the CdS-NP and PbS-NP cytotoxicity for cardiomyocytes. Conclusion. The general rule is the variability of the dose-response dependence types manifested in different cytotoxic effects of nanoparticles.