ALDH1-positivity was associated with chemoresistance in ovarian cancer cells and tumor tissues. A. ALDH1 mRNA expression by qRT-PCR in various chemoresistant SKpac sublines. Relative expression levels are normalized to parent SKOV3 cells. B. ALDH1 mRNA expression by qRT-PCR in chemoresistant ovarian cancer tissues was significantly higher than that in the chemosensitive group. C. To verify the role of ALDH1 in ovarian cancer, we analyzed the correlation between ALDH1 mRNA expression and clinicopathological parameters, including clinical stage, lymph node metastasis, and distant metastasis. Patients were classified into high (≥2-fold) and low (<2-fold) expression groups for comparison. High ALDH1 mRNA expression was significantly (p = 0.019) correlated with advanced clinical stage.