Abstract
The measurement of metabolic activity of target cells after the effector phase of the assay provides an improvement over the conventional 51Cr-release assay. The assay provides a quantitative value of cytotoxicity dependent on the numbers of surviving target cells. The assay described circumvents the inherent problems of variable uptake and spontaneous release of label found in the 51Cr-release assay. Furthermore, 3H-uridine is a more useful label in that its half-life is considerably longer than that of 51Cr.