Concerns about potential health hazard of nanomaterials are growing. To determine the potential toxicity of metal oxide nanoparticles, human SH-SY5Y neuroblastoma and H4 neuroglioma cells were exposed to Fe2O 3, CuO, and ZnO nanoparticles and their metal ion counterparts (Fe3+, Cu2+, and Zn2+) at a concentration range of 0.01-100 μM for 48 hours, under the cell culture conditions: 95% O 2, 5% CO2, 85% humidity, 37°C. Their ensemble cell viability was determined by MTS cell proliferation assays. A live/dead cell assay was also performed, and cellular images were acquired by a high-content fluorescence microscope and quantified by a novel computerized image analysis protocol. Our data indicated that exposure of these nanoparticles induced differential toxic effects in both SHSY5Y and H4 cells, and the cells had dose-dependent toxic responses to the CuO nanoparticle insult. In conclusion, toxic responses of the nanoparticles are complex, and they warrant further in vivo studies.