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(1) Background: Helleborus purpurascens Waldst. &amp, Kit. (hellebore) is a plant species found mainly in Balkans and the Carpathians, and it is traditionally used for a variety of ailments since the time of Hippocrates. The aim of this study was to investigate the immunomodulatory effect of hellebore extracts correlated with relevant chemical compounds and the extraction method. (2) Methods: A methanolic (H1) and a hydroalcoholic extract (H2) were prepared by standard methods. Qualitative (HPTLC) and quantitative (HPLC) chemical analysis were conducted to reveal the ecdysones and polyphenolic compounds. In vitro studies were performed using rat macrophages, murine fibroblasts and immortalized human T-lymphocytes, and their viability was determined by MTS assay. In vivo studies involved a rat immunodepression model. (3) Results: In vitro assays revealed the stronger effect of H2 on cellular proliferation, compared to H1. In the in vivo assay, H2 revealed an immunostimulatory effect in the context of experimentally induced immunosuppression with dexamethasone, a superior effect to levamisole treatment according to the same regimen, in two doses every 24 h. There was no correlation between pharmacological effect and the reference compounds evaluated. (4) Conclusions: The immunomodulatory effect of methanolic and hydroalcoholic hellebore extracts is not due to ecdysones and polyphenolic compounds, but other polar substances, possible steroid glycosides.