In this technical note we provide data useful for the clinical application of the target-induced Natural Killer (NK) loss (TINKL) assay. The TINKL assay is a sensitive flow cytometry-based assay for measuring NK cell function. Loss of NK cells from the lymphocyte gate occurs following culture with K562 (the prototypic target cell for natural killing) and antibody-coated target cells (for antibody-dependent killing). By analysis of multiple samples of PBMC from single donors we document the intra-experimental variability and the inter-experimental variability of the assay. The intra-experimental coefficient of variation (CV) was on average 11% for natural killing and 3% for antibody-dependent killing, compared to 14% and 9% respectively for the inter-experimental variation. Analysis of a 123 normal healthy adults shows large variability in the functional capacity of NK cells in the population both for natural killing (CV 33%) and antibody-dependent killing (CV 27%).