This protocol describes the monitoring of nanoparticle treated human hepatocarcinoma cells (HepG2) for apoptosis, as part of the in vitro NCL preclinical characterization cascade (1, 2). The protocol utilizes a fluorescent method to measure Caspase-3/7 activation. This is a homogeneous assay that does not require cell isolation, as required for HepG2 Hepatocarcinoma Apoptosis Assay (NCL Method GTA-6).