6-Hydroxydopamine (6-OHDA) is a widely used neural toxin in the pathogenesis research of Parkinson's disease (PD). In this work, we have studied the effect of ethanol on the toxicity of 6-OHDA on PC12 cell and SK-N-SH cell. Ethanol alone had little toxicity to these cells. However, if using 40 microM 6-OHDA along with 400 mM ethanol on PC12 cell or SK-N-SH cell for 24h, there was much more cell loss than using 40 microM 6-OHDA alone when detected by 3-(4,5-dimethylthiazal-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay or flow cytometric assay. The toxicity of 6-OHDA was enhanced only if using at least 200 mM ethanol, and the cell loss was increased with the increase of ethanol concentration. We had also found that ethanol could enhance the toxicity of 6-OHDA only when using ethanol and 6-OHDA at the same time, ethanol treatment either before or after 6-OHDA treatment did not show such effect. This effect of ethanol suggests that ethanol may contribute to the degeneration of dopaminergic cells.