Abstract Reliable measurement of cellular cytotoxicity is essential for the characterization of immune responses and for the monitoring of antibody treatment efficacy. Until now, the standard chromium 51Cr-release assay has remained the sole sensitive assay that measures cellular cytotoxicity. Alternative non-radioactive assays have been developed but they do not provide accurate measurement of target cell cytotoxicity. The cost and hazard of handling radioactivity are strong incentive to find alternative solutions to 51Cr. We took advantage of the recent development of cell-imaging multimode readers to develop a novel non-radioactive and real-time cytotoxic assay that demonstrates good reproducibility and sensitivity. The extent of target-cell cytotoxicity is monitored over time by imaging and quantifying live fluorescent target cells in 96-well plates using the cell-imaging multimode reader Cytation™ 5 from Biotek. We have developed classical NK cell assays in the presence or absence of blocking antibodies and antibody-dependent cell-mediated cytotoxicity (ADCC). We show that in these assays, cell killing occurs within the first two hours with a half maximum killing reached after 30 minutes. This technology has numerous applications such as NK and T cell cytotoxicity assays and can be extended to cell survival and apoptosis measurement assays.