Quantum dots are semiconductor nanoparticles with unique, size-tunable optical properties. Owing to these properties, these nanoparticles are fast emerging as versatile and multimodal agents in diagnostic imaging and drug delivery applications. In the past decade, their interaction with various biological models, ranging from isolated cells and tissues to small animals, has been extensively investigated. However, along with the various beneficial effects, the presence of heavy metals in most quantum dots has led the scientific community to view the biomedical applications of quantum dots in a more cautious manner. One potential deleterious effect of quantum dots is triggering or exacerbating the process of oxidative stress, which can interfere with or destroy key biomolecular components or processes in the body. This can lead to premature ageing or diseases such as dementia and cancer. In this chapter, we describe various in vitro techniques which are fundamental in investigating the oxidative effects of quantum dots following their internalization within cells in culture.